Had a '99 Cummins that had an issue with Transmission. It started downshifting out of overdrive for no apparent reason. Took it to the dealer and they promptly said it needed a transmission, $4K.
Just didn't seem right to me, plus I said if this one failed I wouldn't replace it in kind , I would bulletproof one. Did some research and found a TSB from Dodge that applied. Called for a computer reflash to deal with electrical interference from the alternator. Printed it out and marched back to dealer !
Service writer called manager " look at this, he's got the TSB!" (Technical Service bulletin). They got on the computer and poked around for a bit, nope that's not your problem your VIN doesn't come up. Told them that is exactly what my truck is doing. Nope wouldn't budge.
Then they tell me it's my two way radio and emergency lights causing the interference and they wouldn't even look at it until I removed all of it !
Got talking to a friend of mine that is pretty smart in such matters and he asked if my stuff was connected at the battery ? I said it was. He said disconnect it there and go back. "You are now carrying Lights and a radio which is an acceptable use for a pickup" !
When I got back to the dealer they said " We found your truck , we didn't scroll down far enough " !
They flashed it, problem solved for quite a while. By the time it did it again I had found a diesel specialist that said , oh yeah I just put a noise filter on it you'll be all set, and I was !
The dealer would have replaced the transmission and stuck me with the bill due to their incompetence, sure made me apprehensive about going back to them.
I did go back and look at nice looking new Dodge / Cummins a while later, couldn't come to a deal but it sold to a guy in town. Few years later the rust on that truck was just discouraging.