Part II, Chapter XXXVI: "Bat Out of (Development) Hell"
“For a while, we really weren’t sure if it was going to be made at all. We had the Writers’ Guild of America strike in ‘88, then Nimoy was busy. When he came back, we couldn’t get the story to a point where everyone was happy, and eventually I decided to change it drastically. That delay did do us some good though, it allowed us to get Sean Connery as Sybok, and it meant that we could work with Industrial Light and Magic.”
- William Shatner speaking about his role as director and writer for Star Trek V: The Final Frontier. 
The fifth film in the Star Trek franchise was originally planned to be released in 1989, but would take four more years due to various behind-the-scenes events. The end result was that the story was changed drastically from William Shatner’s original plan.
The delay did much good for the film, however. The original release date would have seen it compete with Indiana Jones and the Last Crusade, Ghostbusters II and Batman, all commercial successes. While it was now up against Jurassic Park and The Last Action Hero, it was part of an already established franchise with a large fan base.
Star Trek V: The Final Frontier was released on June 18th, 1993. It received largely positive reviews, with many critics noting that the film was “well worth the wait”. Particular praise was given to the performances of Sean Connery and the actors of the three ambassadors.
Plot Synopsis for Star Trek V: The Final Frontier: (based on a proposal by @Ogrebear) 
The crew of the Enterprise take shore leave on Earth following the Enterprise-A’s poor shakedown cruise. Captain Kirk camps at Yosemite National Park with Dr. McCoy and his First Officer, Spock. Their stay is interrupted, however, by an urgent order from Starfleet, telling them that three ambassadors have been kidnapped on Nimbus III, “The Planet of Galactic Peace”. The ambassadors represent the Federation, the Klingon Empire and the Romulan Empire on the planet, in an attempt to prevent diplomatic incidents. As the Romulans and Klingons hear of the kidnapping, they also send ships to rescue the ambassadors. The Klingon captain, Klaa, also hopes to gain glory by besting the Federation in battle.
Upon arriving at Nimbus III, the crew find that the planet has undergone a sudden change in climate. What was once a lush world is now nothing but desert. Resolving to find out why later, the crew begin planning a rescue mission. They are unaware of the identity of the kidnappers, and so prepare for heavy resistance. Kirk decides to lead the team, leaving Spock and McCoy on the ship. The team manages to break into the compound where the ambassadors are being held, finding very few guards beyond some Breen mercenaries. However, the team soon find themselves under attack psionically, and Kirk is captured while the rest of the team is forced to flee.
Kirk is introduced to his captor, Sybok. Sybok reveals that his kidnapping of the ambassadors was a plan to get a ship to Nimbus III, on which he had been stranded. Sybok also reveals that he has vast psionic powers to inflict pain, on a planetary scale at the limit of his powers. The devastation to Nimbus III was also to act as proof of his strength to observers. Sybok decides to torture Kirk, forcing him to relive the destruction of the Enterprise. Back on the ship, the rescue team returns, informing Spock and McCoy of the kidnapper’s identity. Spock recognises Sybok as his estranged uncle, exiled from Vulcan when he refused to suppress his emotions or psionic powers. The Klingon and Romulan ships arrive, leading Spock to task Sulu and Chekov with finding a way of together with them to free Kirk and the ambassadors. 
Kirk works with the ambassadors in organising a jail break, confident that his crew will send another team down to take down Sybok. In this time, the ambassadors get to know each other better, finding that “more unites them than divides them”. On the Enterprise, neither the Romulans nor Klingons seem interested in a joint raid on the compound, as the Romulans see no political benefit in the move, while the Klingons refuse to work with a species as “weak” as the humans. Klaa is then surprised when Crewman Keyes challenges him to an arm wrestle, besting him. Meanwhile, Uhura and Spock speak with the Romulan captain, Commander Reval, convincing him that it would be in the Romulan Empire’s best interests to work with the Federation and Klingons. With both the Romulans and Klingons convinced, Spock begins planning the new rescue.
Sulu is placed in command of the Federation forces, “as preparation for his new command”, while Klaa and Reval lead their respective forces. Sybok takes Kirk to torture him more, hoping to learn the Enterprise’s transport codes so that he can escape. This time, he makes Kirk face his fears that the crew will be broken up by Sulu’s imminent promotion, and reassignment to be given his own command. While this occurs, the ambassadors, led by Korrd, are alerted to the arrival of the rescue party by the sounds of phaser fire. They use the opportunity to break out, joining the rescue team. 
Sybok realises that the prisoners have been freed, but that he now has a way to the ships via the shuttles. Sybok stops torturing Kirk, unleashing a wave of psionic energy that momentarily incapacitates the attacking forces. He creates psionic illusions, disorienting them further, and escapes to the Federation shuttle in the confusion. Unbeknownst to him, Spock is hiding there, having anticipated Sybok’s moves. Sybok starts psionically attacking Spock, insisting that “no Vulcan could best me”. Spock counters with a kick to the groin, remarking “It is good then, that I am half-human.”
The crews return to their ships, remarking the détente that they achieved could set an example for how Nimbus III should work. On the Enterprise, the crew celebrate one last night together before Sulu is given his promotion, breaking the team up.
Cast of Star Trek V: The Final Frontier:
- Captain James T. Kirk – William Shatner
- Spock – Leonard Nimoy
- Dr. Leonard McCoy – DeForest Kelley
- Montgomery Scott – James Doohan
- Hikaru Sulu – George Takei
- Pavel Chekov – Walter Koenig
- Uhura – Nichelle Nichols
- Sybok – Sean Connery
- Crewman Keyes – Michael Clarke Duncan 
With a positive reception to Star Trek V, a sixth film would be greenlit. With The Next Generation drawing to a close, plans for the cast of that show to take over the film franchise would begin to be made, and discussions about the sixth film serving as a “handover” would become more commonplace. 
 The four year delay over OTL means that ILM isn't busy with Indiana Jones or Ghostbusters II, and Sean Connery isn't busy with the former.
 Many thanks to you @Ogrebear for your suggestion a few pages back. As you can tell, I've used most of them.
 I want to clarify Sybok's powers here. His power to "remove pain by making people relive their fears" is sort of reversed. He makes them relive their fears and regrets, siphoning their "mental strength" off of them. To begin with, he didn't have the power to cause an extinction-level event like he does with Nimbus III, sparing those in the compound so that he has hostages, but the more he feeds off of, the stronger he becomes. His plan is to go back to Vulcan and take his revenge on the Vulcans for exiling him.
 Sulu's command is brought up earlier, as the possibility of this being the last TOS film is a very real one.
 This would be his first major acting role in TTL, but he was looking for work at the time. He may come out of the bodyguard field earlier if this leads to anything. Also, this list is mainly so that you can see the major casting change, if it wasn't already obvious.
 OTL's Star Trek VI has been butterflied.
My apologies if the plot synopsis seems a little fuzzy at times, I was trying to fit a fair bit in, but I changed my mind about a couple of things at times, or realised I'd forgotten something. I may come back at a later date and give it a polish. Once again, my thanks to @Ogrebear for your brilliant plot suggestion. I only wish I could see this on the screen, but alas, that is the burden of being a fan of alternate history.