Stumbling 94 Chevy
 

I have a 94 Chevy 1/2 ton 4 wheel drive pick-up with a 5.7 liter motor and it runs great. Most of the time. This truck has about 130,000 miles on it. As I said, it runs great, until I start up a hill and lug the motor. Then it will start with a stumble and does this all the way up the hill until it shifts down to another gear. The stumbles, a miss to me, are about 2 to 3 seconds apart until it shifts. It has, also, done this a couple times while stopped at red light. But, at the stop light, the miss or stumble, is about 5 to 10 seconds apart. No codes in the truck computer. So, I'm lost with what to look for. Any ideas? Also need to add, the motor has TBI and I added some injector cleaner to the gas tank with no help there.

Have you checked it for vacuum leaks? Make sure you check the TBI to intake mounting flange gasket as well. Check the vacuum line that's going to the map sensor, make sure it's pulling vacuum as TBI engines were bad about gumming up the throttle body so bad with carbon it would plug the vacuum ports. Also what shape is the tune up in? When was the last time it was tuned up?

That is typical of needing new spark plugs. If you buy the platinum plugs (about $8.00 ea. in my area) and gap them at .045 for an HEI ignition, the problem will go away. Been there, done that.