Got a 90 Silverado that is running poorly...It runs a bit like it has a very heavy trailer behind it. Doesn't seem to be missing but chugs along done all I can think of but still no change. 02 sensors fuel pump map sensor. there is one thing that is odd if the turning signal is flashing runs fine if I hold the window up botton it also runs fine does any one have any ideas where to go from here?

 

Bad ground.

Allan

 

Yep Go to full size chevy.com and do a search they come up with a ground kit for problems like this. Too lengthy to explain.