Well it started up almost instantly today, after refusing to re-start last night after it died. It was acting exactly like the battery was dead last night but cranked and fired today no problem.

I checked the fuel tank vent and it seemed ok. I took it off completely just to be sure. Just like before, it idled nicely and had low power, but could at least cruise very slowly around the block. However, once it gets up to temperature, it looses the small amount of power it has and just creeps along (~5mph max), then starts running really rough, slows down to a stop, and dies. When trying to restart, it very slowly cranks and won't start, just like a dead battery situation.

I have not measured the turbo boost, as suggested, but I feel like I have bigger problems considering it won't even stay running after it gets hot.

I'm out of ideas, I've tried everything people have suggested. Any idea on what would cause it to act like it has a dead battery once it gets warmed up? I do not think it is overheating, the temp gauge only gets up to 90C. Thanks.