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97 GMC Sierra Transmission?

I do 99% of my driving in town. In town I have no problems driving around. The problem is when I go on a road trip of at least 2 hours. After being on the road for two hours the RPMs suddenly go up and my speed drastically decreases. I have to have very high RPMs just to keep the truck at 55 to 60. It did the samething on the return trip home after driving for two hours.

Do I need a transmission rebuild or could it be something less expensive?

Advice much appreciated.

I had something similar happen to me on the same model truck about 10 years ago. It was still under warranty then, so the dealership went on and replaced the whole transmission. However, I do recall they said the torque converter had simply gone out. You may want to have that checked out first. Good luck.

Did you at least check the fluid level and condition (i.e. color/smell?) I would do that first. Of course, if you’re low it means hoping that you haven’t burned things up yet and having the leak fixed.

I would take it right away to a trans shop and let them scan it. Either the computer is putting the trans into limp mode because it has detected a problem or, considering what you say about very high RPM’s to maintain 55mph… Its entirely possible the 3-4 clutches are shot. My best guess would probably be limp mode since 3-4 failure would mostly cause a neutraling condition. Or, a solenoid failure. Either way, a scanner needs to be connected and the computer monitored to see when and if the computer is commanding the 2-3 and 3-4 shifts. As always, check the fluid level and condition.
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Thank you very much for the replies.

The first time it happened I had the transmission fluid replaced. I took it on 90 mile road trip and it did it aqain. The fluid smelled ok before it was changed.

I drive every day on the freeway without problems it is only on extended trips of 90 miles or more.

I am taking the truck into the shop to have a fuel pump replaced and will take into have the transmission checked after that. It is paid for. I don’t mind having it fixed especially in this economy.

Thanks again.