I've got a 91 F150 with a 5.0L manual with dual tanks. One the first tank all is fine and dandy, but on the second tank it drives real crappy. I get a lot of stuttering and no accelleration. Almost like shifting without enough RPMs. If I shift in to gear with it at least 2500 RPM or higher I have less problems.

This only seems to effect the 2nd tank as I said, 1st is fine.

 

Alot people don't use the second tank very often.
My guess is that you have stale gas or dirty gas in there.
You need to get the old gas out of there and its probably crudded up the in tank pump.

Just a guess

 

Or the pump in the second tank is dying.

 

I've got this same problem with brand new gas

 

I was talking to a mecahnic friend and off the top of his head he was leaning towards the in tank fuel pump also. Labor and parts could run $300+ for it, so I'm guessing I'll be running on the front tank till I can put out cash for a new pump and parts.