I have a '93 gmc sierra 1500, 5.7 , manual trans and the following problem. When i'm trying to maintain a constant speed and the engine rpm's are around 1500 the engine bucks like crazy. Under a load it's fine. Or if i remove my foot off ther accelerator it's ok. Could it be a vacuum leak? There is 156,000 mi. on her. Replaced the tps to no avail. no check engine light. plugs wires cap all ok. very frustrating.she's making me crazy. any and all input is appreciated. Thanks JR
