Jimmy Idles fine, but when driving...

I have a 92 GMC S-15 Jimmy 4.3L. I started having this problem in about October, my Jimmy has been sitting all winter, and now that it's warm again I'm back to workin on it.

It will idle fine, but when driving down the road, it sputters. Most time at wide open throttle it will not sputter, but does almost all the time at low revs, but when stopped, will idle fine.

I first thought rust go in the tank, or the fuel pump was going bad.I removed the tank, no rust, and put a new(well...different...from the junkyard) pump on, and I have the same problem. It seems that the longer it sits, it gets better, but the more it's driven, the worse it gets.

I was wondering how I could tell if it might be the fuel pressure regulator, or how I could tell if it is the nut kit(or whatever it's called) Inside the intake manifold. And how does a vehicle act when the nut kit needs replacing?

u cant have 2 threads going about the same topic. use the one in the blazer problem diagnosis since that gets more traffic.