1999 GMC Suburban Ls, Rough Shifting after warm

[RodneyB]

Hello,

I have a 99 GMC Suburban LS 4x4, auto trans. I just bought this truck and previuos owner had it sitting for 5 months. I have put 350 miles on the truck.

It shifts smooth as silk when running 20 minutes or less. If I run it longer, I get very HARD shift on 1st and a medium HARD shift on 2nd. Truck has 173k miles.

Trans fluid looks good and does not have a burned smell.

What steps should I take to resolve. Do the Trans coolers go bad and need to be replaced? Do I need to get a trans flush ?

Any help would be apprecaited.

Thanks,
Rodney

 

[Molson02536]

Hello,

I have a 99 GMC Suburban LS 4x4, auto trans. I just bought this truck and previuos owner had it sitting for 5 months. I have put 350 miles on the truck.

It shifts smooth as silk when running 20 minutes or less. If I run it longer, I get very HARD shift on 1st and a medium HARD shift on 2nd. Truck has 173k miles.

Trans fluid looks good and does not have a burned smell.

What steps should I take to resolve. Do the Trans coolers go bad and need to be replaced? Do I need to get a trans flush ?

Any help would be apprecaited.

Thanks,
Rodney

Replace your Boost valve and sleeve, there about $50.00 and installs in about 10 min when servicing the transmission fluid and filter. The cost should just be under $175.00 and do not flush your transmission.

What is happening is the boost valve is getting weak and the EPC valve is trying to compensate for is but rising the Transmission fluid pressure which is causing the Hard shift when the transmission heats up.

Good luck and keep us posted.