Yeah, maybe they pull out of that poorly conceived Northern invasion sooner, and find some way to regroup in 1864. Or maybe Meade destroys the ANV instead of wounding them as Grant did, opening Virginia. All in all, not the most interesting PoD.
Not much different than OTL. The Army of Northern Virginia ends up mauled and exhausted after days of assaulting an entrenched enemy who's dug into a solid defensible position. Doesn't matter whether it's at Pipe Creek as OTL or a contrafactual where the Union somehow manages to get hold of Cemetery Ridge on the first day of battle of an extended (and multiday!) Battle of Gettysburg, Lee's army is left with no choice but to abandon the field due to being bled white.
Longstreet hopefully escapes with his reputation in better shape, though. Can't possibly be worse than the tarring and feathering his alleged defeatism at Pipe Creek has wrought from the Lost Causers.
Now that I think about it there's an interesting ripple I can see from this. Might John Reynolds end up in charge of the war effort? IIRC he was the only general besides Winfield Scott who performed well during the battle. Remember that Lincoln wanted Reynolds instead of Meade before the battle to take over the AoTP. Instead Meade ended up getting sacked due to his failure at Gettysburg even though he was instrumental the defense of Pipe Creek with Grant replacing him and taking charge of the whole army after Vicksburg ended.
If Gettysburg is a Union victory it could save Lincoln a reelection. The troubles and Union infighting before and after the election prolonged the war by at least 3 years. the South gained much breathing time with this victory. War over in 1866 or even 1865 could also mean the US has enough time to prevent Maximilian to defeat Juarez and the other republican uprisings. The Texans probably would not ask for readmission to Mexico. California and the Nevazona Territory would not been lost to the Austro/French/Mexican Alliance in the 1870/71 war when the US tried unsucessfully to reclaim Tejas. (OTOH France could prevent the forming of the German Empire if not distracted in America).
Going further the US wich incorporated those lost territory (and had not to pay so much for the lost war) would probably be ranked number 1 and not 10 among the "great Nations".
Looked up the 2015 edition of the Evidenzbüros "Handbuch der internationalen Beziehungen": The current ranking is:
1. British Empire and Commonwealth
2. French Empire
3. Greater German Co-Prosperity Zone
4. Russian Federation
5. United States of Greater Austria and Croato-Hungaria
6. Japanese Peoples Republic (including the PRK, Manchukan Communist States, Phillipine Peoples Republic and Indonesian Islamic Peoples Republic)
7. Chinese Republic
8. Mexican Empire (including in a strictly ecomomic sense the South American ECOSUR)
9. Federation of South European Catholic States (Spain/Italy/Portugal including overseas posessions
10. United States of America
The SECS might drop out of this list as their internal quarreling will likely lead to breakup and the Panturkish Federation might be again counted in the big 10 after their dropout in the 70s.