Redbeard, I don't expect Germany to match the USA, nor do I expect them to get rid of horses, or replace railways. What I do expect is, since their industrial base was 40% larger than Britian's in 1938 and 70-80% in 1941 that Germany produce about 60% more trucks than Britain, that would be about 770,000 trucks during the war, or about double of OTL. OR!!! Since Britian's army was about 55% of it's armed forces strength, and Germany's was about 80% Germany should have put a greater proportion of it's larger industrial base into land forces equipment, so this should push truck production up further, (in lieu of a German need for Corvettes, landing craft, escort carriers etc) perhaps to One Million trucks throughout the war, or triple OTL. In such a scenario deisel is mandatory to stretch oil consumption as far as possible.
With double or triple the trucks available to Germany (in theory, it would never happen, but for argument's sake since it brings Germany into line with the UK and US industrial performance) a number of options become open to Germany. More Mot. inf. divs can be formed, to push infrantry up with the panzers, more support can be given to the Pz. divs and an array of other transport shortfalls within the 1941-2 Wehrmacht could be addressed. But mainly Barbarossa could be launched earlier, the mobile spearheads could be made much stronger even if they don't go any deeper, and the handful of km to Moscow could be achieved before winter.
The answer to Germany's problems do not lie with more horses, it lies with more trucks. If they had more horses we'd be talking about the shortfall in fodder supply, and how horse feed took up so much rail capacity even through the rains had stalled all movement, etc.