A failed MAP sensor will cause the idle to be poor, and the fuel mix to wander without reason. At idle it will run fine for a second, and then stumble and jerk, and then run fine once again.
EGR would likely cause stumbling and 'trailer hitching' while traveling down the road, as would failing plug wires, or very poor idle. You can test for EGR function by moving the EGR valve by hand at idle. Push on the diaphragm from the valve side, or apply vacuum and watch the idle go bad. Release, and it should smooth out. Disconnect and plug the vacuum line to road test, but don't leave it that way or you'll get pinging.
Water in the fuel would cause misses and stumbling going down the road to where you would think the engine had lost its spark. Run fine, then seeming dead miss and no response to throttle input for a few seconds as it tries to run on water. It would be most noticeable after heavy braking, going around a sharp curve or going up/down a hill where the water would move out of the lowest spot in the fuel tank, and get ingested by the fuel pump.
A failing main relay would disable the computer, and interrupt the fuel injector operation.
If it runs well, no miss, full power, smooth acceleration and idle, and then goes nuts, chugs, misses, and falls on its face, I'd suspect fuel contamination. Some urge the use of Seafoam to absorb water in the fuel tank, and that is one solution. I've done it once with some success, but am getting the problem back.
When you accelerate, and go to shift gears, taking your foot off the gas pedal, the engine will drop rpm's significantly, making smooth shifting difficult IF the engine is having fuel problems. At least that is what I think I am having. It is as if the engine does not want to run like it used to, and jerkiness is its new mode of operation. I am going to inspect the fuel filler hose for damage, as I might be getting rain water into the tank.
tom