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Discussion Starter · #1 ·

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 500 miles on the truck.

It shifts smooth as silk when running 30 minutes or less. If I run it longer, I get a 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.

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