Engine Misses in 4th and 5 gear

[Blakbat]

Does anyone know why my v-6 88 4x4 would run fine through third gear and once in 4th, and the RPMs are under 2500, the engine would run rough. It is really baffling and I want to fix it. Having it miss in irritating to say the least. When in 4th, rough, shift to third and the RPMs rise to over 3000, it smooths out. Any Ideas?
Jeff

[smasheromalley]

Possibility that it could just need a tune up. plugs/wires/cap/rotor

It takes more horsepower to move a vehicle in 4th gear than it does in 1,2, or 3rd gear. This requires you to use more pedal. More pedal puts more air and fuel into the cylinders. More air and fuel means higher cylinder pressures. Higher pressure in the combustion chamber creates higher resistence between the spark plug gap. Higher resistance means the spark is more likely to find another path to ground like down some carbon tracks or arc through a bad wire.

Hmmm, thats a theory...

Does it miss if you accelerate hard through low gears?