99 jimmy auto transmission shifting

My 99 jimmy auto trans will shift with a clunk when shifting from 1st to 2nd early in the morning. It feels like it shifts from 1st to 2nd then back to 1st and so on for about 75 yards. After that the car runs fine the rest of the day, until the next morning. There are no trans or engine codes. The filter and fluid was just changed. The tranmission repair garage said it is an engine problem. The engine repair garage said it is a trans problem.

How many miles since the last tune up, (plugs, plug wires, distributor cap and rotor) using AC Delco parts?

How long do you warm up the vehicle before moving it? It can make a difference.

Did the engine shop scan for/monitor the transmission data or just blame it on the trans? I'll bet the trans shop scanned both (unless it's a chain like Aamco).

How many miles since the last tune up, (plugs, plug wires, distributor cap and rotor) using AC Delco parts?


Complete tune up about a month ago. This dosen't feel like a missing engine, but it is drive train related

Complete tune up about a month ago. This dosen't feel like a missing engine, but it is drive train relatedmmmmmpppp

Sometimes it can be difficult to distinguish between engine and transmission problems, even for a "seasoned veteran" technician. A good technician that knows how to read, and understand, the scan tool will be able to spot the problem. If the power going into the trans is not smooth, output will not be smooth... junk in, junk out. If the trans has a problem with an intermittent shift solenoid, usually it will set a DTC in memory. If the engine has an intermittent random misfire caused by a fault in secondary ignition, it might not necessarily set a DTC. The 4.3 is very fussy about tune up parts, just out of curiosity, what brand of parts, (plugs, wires, cap & rotor) did you use for the tune?