Perhaps its time to get away from the dealer.
Is P0446 the only code you have right now? Its not going to make the car lurch or lose power. If they are telling you that you need a new transmission I assumed that you would end up with some transmission-related codes.
Have you actually checked the transmission fluid on your own? It should be at the proper level, a nice translucent red, and not smell burned.
The two things on the top of the list for lurching/power loss under acceleration are fuel pressure and exhaust blockage. It is certainly possible that its a transmission problem but I wonder what led to this conclusion.
You said your mechanic tested the fuel pressure static & cold. It ought to be checked hot and under load. Someone should also put a vacuum gauge on it to check for exhaust blockage - unless you have some more info about the transmission.
As much as you can’t drive around with the evap system throwing codes, there’s no point in putting money into that if you have much larger issues.