i have a 89 4.0 HO that sputters and backfires when steady driving between 1500-2000rpms, but if you are accelerating it has no problems

i have changed plugs, wires, coil, module, CPS, distributer, cap, rotor, checked vacuum lines for leaks, seafoam in the tank, replaced fuel pressure regulator, and fuel filter twice

thats what i can think of right now, i may have done some more

i got this jeep from a friend of mine and it had been sitting for 2-3 years and it did have about 1-2 gallons of bad gas in it, well i haven't drained the tank, but it has had 2 cans of berrymans b12 and a can of seafoam in the past 3 tanks, but yet i still have this problem

PLEASE HELP I AM STUMPED