If that's the motor I think it is, it is the 5.7L "P" motor (8th digit of the vin will be a "P") If so, then it sounds like the Optispark Distributor is having it's common issue. The vent tube on those used to get plugged, and then the optical disc inside flexes on acceleration and causes this problem. You can try to clear this by removing the vent line and CAREFULLY shooting compressed air into the vent hole to remove the debris. If this does not work, then you'll have to remove the cap and rotor (and replace them) and clean the vent from the inside. Unfortunately, this means removing the water pump as well, and it should be replaced when you have it off. Bad design.