I have a 2000 S10 automatic with about 110k miles on it. Last week we had a cold snap with nightime temperatures dropping to about zero and daytime running in the single digits. The truck began running rough during that period of time. I put gasline deicer and injector cleaner through it with no improvement. The truck starts fine, accelerates ok, but when cruising it seems to “lurch” with the engine reving slightly, then dropping back to normal rpm. Weather has warmed into the low 40s and the problem has gotten better but still persists. Any suggestions?
The list of possibilities is pretty long. The place so start with things like this is always to make sure that the basics are taken care of - are all basic maintenance items up to date? Spark plugs, wires, air & fuel filters at minimum. A check of the fuel pressure under load would be in order. A search for vacuum leaks wouldn’t hurt though that kind of problem would mostly show up at idle. Cleaning the throttle body and mass airflow (MAF) sensor would be a good idea - might not help but it can’t hurt (as long as you’re careful with the MAF).
The slight rev up and then back down could also suggest a torque converter lockup problem with the TCC locking & unlocking. That can come from internal problems in the trans. It could also be related to a failing throttle position sensor among other things. The TPS is pretty easy to check with a multimeter and specs from a repair manual. Has the transmission been serviced as it should over the 110K?
Is the check engine light on? If so, have the codes read and that can give you a starting point.