Visitoron Dec 7, 2010
Common problem with seemingly multiple causes which I myself am gradually going through....HOPING that I don't end up having the most costly... that being transmission/TCC/TCC Solenoid related.
Along the diagnosis path I've discovered a Throttle Position Sensor that was bad, a Crank Sensor that had occasional hicups (only showed when I really forced and encouraged the shudder problem), a fuel filter that was dirty, fuel injectors that needed Techron, plug wires that were long overdue for changing (plugs were changed a couple years back and should be fine), checked the ignition coils and found them ok, and engine vaccum can also be called into question.
And after all this I have found improvement in the engine's ability to deal with power under load....but NOT solved what is a definately SHIFTING related shutter around 50-60.
So the next stop is a transmission repair place which I trust. Everything else I've done myself (which I could also verify the vaccum is fine).
So my advice is to do the kind of things that you'd do to "tune up" this engine. Make sure fuel & ignition are happening the way they should be. Then start considering the transmission. Good Luck... I'm no expert...but I've been down a similar road.
BUT ass
Thanks! I had done most of the things you mentioned prior to asking the question: plugs, plug wires, fuel filter, tested the Throttle Positioning Valve, and put LOTS of injector cleaner into the gas tank. Ironically, the only thing that seemed to help was the injector cleaner - but only for short periods of time, anywhere from days to weeks. I have since sold the vehice and truly hope the new owner, a female whom I had made aware of the problem, is not having the problem I was experiencing. A local mechanic told me it was possibly the torque convertor. I hope that is not it!!
Following up. I'm the Dec 7th reply and I've since found that my checking of the ignition coils was NOT adequate. They WERE indeed the problem. They were "in spec" but dissimilar in resistivities which is either bad in itself OR indicative of one or more of them being bad and not able to hold up under load. I changed the three out and presto....problem solved!!!! Man was I fearing the transmission TCC solenoid was failing.