idles great, runs rough when driving

[sect8dr]

got an 89 with a 2.9, 5 speed, factory t-case, and dana 44 front, and 9 inch rear with 38.5 tires. Lately it starts up fine, idles great but when i hit the throttle it does not want to run, it spits and sputters and falls on its face. There is a sweet spot with the throttle pedal, when you find this sweet spot it will run great all the way to 65. i can't figure it out thought maybe someone on here could give me a clue

[Ranger Dave]

38.5 tires,what gears ya got

[sect8dr]

4.88 for now going to either go lower in the axles or in the t-case soon. It does pretty well considering the lack of power. plus i dont have any lockers in there yet so that helps keep it alive.any ideas on the sputter?

[Ranger Dave]

check the fuel presuure