I have a 2001 Ford Windstar

I have a 2001 Ford Windstar. Background details: The van started violently shaking when I would try to accelorate and going on incline. I had fuel filter replaced and used sea foam. It quit. It ran fine for a while then started doing it again, I used sea foam again and it quit. I thought I was getting bad gas. I started getting gas from a different place that guarentees their gas. It was fine for a while. Then did it again. SO I ruled out bad gas. Got the sea foam again. I couldnt decide what I was going to do. The next morning it ran fine. The morning after that was very cold. When I went to start the car it wouldnt start and I had to pump the gas. All the guages went to max. I knew this was a sign of battery trouble. I took a look and it was all corroded.I did some research and found that a faulty battery can cause problems that seems fuel replated, like a slow running fuel pump or cause an injector to stay stuck open. I replaced the battery and the battery cable connectors. Thinking this would fix ALL the issues I was having. (Also part store check battery and said it was definatly bad) Now, when I am driving and running the AC the van will slightly jerk every so often, NOT just when I turn it on, the entire time I am driving and the AC is on it will do this. It doesnt do it when the heater is on or when nothing is on. It doesnt seem to matter how fast I am going. All fluid levels are good. The jerk is very subtle, at first I wasnt sure if I had really felt anything. I dont know is it is related to the other problems I was having because I have only had the van a month and this is the first time I have used the ac. Please help me. My dad has no problem fixing whatever the problem is but its the tracking it down that is difficult. I am 8 months pregnant with 2 other small children and really need my vehicle running up to par. Thanks!