Would a bad vacuum pump make the pickup spit, sputter, smoke and loose power. Or is it the catalytic converter?
The vacuum pump on the 6.5L engine provides vacuum for operating emission controls, cruise control and heater and A/C servos.
That being said, I do not think the vacuum pump has anything to do with the engine spitting and sputtering or the loss of power.
If the catalytic converter was clogged, it could cause the issues you are having.