Loss power

I have a 91 Astro, 191K, changed the oil, plugs and filled up the gas tank. Nick name the devil, (because of the color) The devil starts up fine, on the first crank. If I am setting in the van push the gas pedtal down in a fast motion the engine would shake and then increase in RPMs. When I hold the gas down a little, hit the gas pedtal and it would bog down and then resume the RPMs. Also if I am going 60mph on the highway and want to increase my speed and hit the gas pedtal or just try to go a little faster then it would bog down and loose speed until I let off the gas a little the speed would climb up, if I am lucky might get 70 out of it. The engine sound like it has power, but the devil does not go as fast as it sounds. All this happened over night. I notice the problem a day after I filled the fuel tank up. No dummy lights come on, I have oil, water and fuel.
Any help on this problem, Thanks

Bad spots in the TPS. Check it with a DVOM, you should get a smooth swing from roughly .5volts to 5 volts through the range of the throttle. Any jumps or drops and you have found the problem.


Do this BTW with the engine off....

Thanks Smalley,
But can you tell me what is TPS, DOVM and were would I find the volts.

Your dealing with a novice