Ford Windstar 3.8 Rough Idle/Hesitation?

2000 Ford Windstar 3.8..

My van has been running excellent up until last weekend. My wife left for a day of shopping and everything was fine. She backed the van into the driveway to unload groceries. When she got back in and started the van it began to hesitate and then stall. Did this 3 times in a row. I then came out and tried to start. It started but gave a good shake. I gave it some gas and the shake went away.

Now we have been driving the van. Sometimes at start it will shake/hesitate but will go away. It never does it during stops or anything. Just at first startup. However when driving it seems sluggish. No check engine lights so no codes as a garage has checked. This evening I start the van and after its started it will idle down but have a light shake like its gonna stall but doesn't. The engine sounds like a diesel engine now. I rode up to Oreillys auto parts and they said to put some seafoam in the tank on a full tank of gas. I'm not sure if I should do seafoam from horror stories. I took it to a local garage where they said since no engine light,the scanner isn't pulling any codes. They said the van has a mind of its own. I asked about fuel filter and they said no because it would give a code if bad. Then asked about spark plugs and wires since its been a few years and they said if they were bad we'd get a code. They think it may be a case of bad fuel or too much water in the tank.

My wife only takes it to one gas station and no problems. ALways topping off at 1/2 tank. She went to a gas station out of town and thinks maybe it could be bad gas. As we are at a 1/4 tank left as she wants to go and fill up. Could this be bad gas?? I'm sorry guys this is driving me nuts. It sounds like a plugged muffler too. I don't see smoke but do get alot of clear water dripping. "Pretty sure just condesation"... Any help would be much appreciated...

(UPDATED) Lastnight I changed the oil and Spark Plugs..Started the van and seems to run okay. Took it for a test drive and came back and while in idle the van started to shake alittle bit.Its almost like it idles really low and the muffler under the van shakes. Give it gas and it goes away..This is driving me nuts.