My truck ran fine for two weeks after getting out of storage then I got a code 21 fought. So then I replaced the tps sensor. It ran fine for about 3 weeks then back to the way it was when I got the 21 code. It has a longer cranking start up. then fires and starts up also fine isles fine for a while then some times idle will raise and lower. Not all the time. Drive ok until you get to 35-45 -50 mph continuous at that speed then you can feel either engine up and down or slight miss or transmission has a slightly chugging. I do not have a tac in the truck. It Feels almost like you have a tire out of balance only at those speeds then increasing speed runs fine.But Then you come to a stopped slow down and the engine just stumbles like it wants to stall. Few times it did but will start or fire right back up quick start up. When running ruff You feel the need to drop it in into neutral and press the gas to keep it running while stopped. Then you can put back into drive and it takes off but with a slight hesitation. Runs decent as long as your pressing the gas peddle. Then again if you get to that consent 35-45-50mph it just feels like engine has that slight miss. It seems to Accelerate decently straight through past the slight hesitation to 5- 65-70 mph. If anyone has any input on trouble shooting is dilemma I’m having I can use some help solving this issue. I do have GM service manuals in hand haven’t come across any thing that is helping. I replaced Throttle position sensor twice. It looks to me like there is no adjustment in the hole position on this years type sensor.
Thanks for any help. Love the truck and want to drive it. I had it to a local non GM garage to help in troubleshooting but no help to me. Truck has 86k on it and ran great the last 3 years. Just started this when I got it out of storage this spring. I Replaced fuel filter new distributor cap button wires and ignition control module and temperature sensor last year. I put fuel treatment in the tanks before I stored it for winter and have ran more then three tank of fuel out in each tank. Thanks for any help Tom
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