Have you tried the following:
Taking Gib and stacking it with German/Italian planes?
What a horrific waste. Destroyed as soon as the US enters the war, and it’s better than killing Axis ground troops for their IPC value.
Building a German Fleet in Z112, taking Gib, and entering the Med?
That’s German troops not on the ground. They’ll never get to Moscow and struggle to defend themselves.
Blocking Z91 US fleet from reaching Italy?
It dies when the US enters the war. If Italy blocks other zones, US air power should be enough to dislodge it, and the planes certainly aren’t needed for the later ground assault. At the worst, the transports break off and land in Normandy for a turn while other US ships clear sea zones.
Having Japan attack North America?
The US is forced to build tanks and planes for a turn. Which end up in Europe as soon as Japan sees how pointless their feint was. As they are getting pushed back in Asia by turning around. Oh noes.
Also, have you tried playing on after Italy falls?
Why bother? US has a steady troop flow that Germany can’t interrupt and can now start building tanks right in Italy. Game over.