I have a 2001 Blazer Lt 4wd. When you try to pass another vehicle, the tach red lines, the vehicle jerks like the transmission doesn't know what gear to be in and the motor sounds like it has marbles in it. After you back off the throttle and drive regularly, the the truck jerks like it was just shut off. No codes come up and I don't see any fluctuations in any of the gauges, except the tach drops then immediately picks back up. Anyone have any thoughts???

 

it could be a bad VSS (Vehicle Speed Sensor) could be telling the ECM to shift at the wrong time, pick one up there only $20

 

Sorry it took so long to get back. Chasing a P0302 and I need to get it through emission inspection. Replaced the switch. Works better but when the tach hits about 4k, it starts acting up again. Thanks for the idea.

 

DO NOT guess what is wrong! Its expensive. Troubleshooting the problem is cheap! That VSS could have been tested.

Personally I have not had this problem so I really cant give you a direction to go. But I can tell you there are people here who will help you troubleshoot it.

Good luck!