Given that the US had all its major ports occupied by the time I'd reached the Pacific(and conquered the US mainland and UK) I would have thought a supply problem should have arisen for the US. As for the air-superiority etc. factors, I had completely destroyed the US air-force by that time(except for the carriers) and it only had 1 IC left - while I had huge numbers of 4-unit squadrons of TACS etc. Also, it was c.1949 by then, and I'd already fully researched all naval combat tech - only the build techs for some of the capital ships such as DDs/BBs etc. was left over.
And I rather doubt the idea that a full-teched up German air-force is able to sink Allied ships. For example, I built up a horde of squadrons of naval bombers to sweep the oceans, and, in 3-4 years of game-time(I put an extreme emphasis on keeping up to date with all air-techs, especially ones involving naval bombing), I only managed to sink c. 3 to 5 ships from the Netherlands(!) - well, OK I did manage to sink quite a lot of convoys, but those aren't real ships, as such. I then was told, at c. 1944 in game-time, that naval bombers had been deliberately weakened to ensure their lack of effectiveness, so I started using my normal planes, in particular the multi-role jet-fighters which I produced later on - and they had no effect on enemy ships, either. By contrast, my subs, which had also been heavily weakened, managed to sink 2-3 ships every six months or so, with one unusual confrontation resulting in the loss of c.30-40 UK ships.
Re full-mobilisation tech:- If the idea is to get infantry fully motorised, shouldn't the increase in speed be +4, rather than +3.3? Then the speed would be 7, which seems about right for a motorised infantry unit.
Other than that, (and the escort-fighters issue which is being hopefully fixed for 0.30) and the constant need to improve the AI of any Paradox game(Japan practically stalled after conquering China, for example), this, my only fully played HOI2 DD game, was quite enjoyable. I got a few nasty surprises such as an Allied invasion of Axis-occupied Norway, and it was quite tough to deal with the US bombing raids on Continental Europe.
Oh, one last thing. Historically, the UK and particularly the US gave vast amounts of supplies, lorries etc. to the Soviets in WWII. I didn't notice any specific event for it, and found the Soviets far too easy to defeat, so, if it hasn't been done already, perhaps an exchange of techs between the US and the Soviet Union could simulate part of this aid-effort.