97 Sierra 2wd Transmission ? Freeway Cruising Problem

[iain42]

97 Sierra 5.7L 100,000miles 2wd

The problem only arises if I am on the free way for 1.5 hours or longer.

Problem: After an hour or two on the freeway the rpms will rise and my speed goes down. It is like my transmission is down shifting. My engine is trying to keep me at decent highway speeds but rpm is high so I try to keep speed down. This never happens in city driving even if I drive aroud all day. This is frusterating but fortunately I don't leave town that often. I plan to get a transmission rebuild after I get it paid off which should be by christmas. Is there a way to fix this particular issue without a rebuild?

Any advice much appreciated.

Thanks!

[maxwedge]

Welcome to AF, to properly diagnose this issue a road test should be performed with a tech using a trans function scanner to accurately diagnose the problem if it trans related.

[Z15]

Could it just be the road/driving conditions forcing the truck to shift in/out of overdrive?

You don't state if this just started or if this is a new truck for you, or you are pulling a trailer, carrying a load, happens on hills etc.

[iain42]

Originally Posted by Z15

Could it just be the road/driving conditions forcing the truck to shift in/out of overdrive?

You don't state if this just started or if this is a new truck for you, or you are pulling a trailer, carrying a load, happens on hills etc.

I have had the truck since 40K. This started happening last year on every road trip over 1hour 1.5hours. I am not carrying a load at all. This drive is between Little Rock and Hope, AR very flat roads. It is like I am thrown from overdrive into another gear possible 2nd maybe 3rd. The rpms required to keep from getting run over on the highway are high don't remember exactly how high but it is like the engine is working way to hard to get me to 60mph.

Thanks.

[slash09]

check your TV cable. your transmission might think you're giving it more throttle than you really are. do you have a locking torque converter? mine would unlock and the motor would spin an extra grand.