1997 suburban trans probblems

My borther in-laws suburban shifts hard when i has been driven for a while, its a automatic, I was thinking it needs a fluid and filter change. Any other possabilities of what it could be.

This usually is an issue with the pcs in the trans. A full trans scan will reveal problems that can cause this.

What is the pcs? Dose the trans half to be dropped and split?

Pressure control solenoid, assumnng this turns out to be the diagnosis, the solenoid pack is accessible with just the pan dropped.

Or the connections to the pressure control solenoid. The main electrical connector on the RR corner of the trans is a potential problem area.

It could be ready to set the P1870 code from a valve body that is worn where the tcc apply piston sets. Quite a few wear and leak fluid by and when the PCM detects enough slippage it commands full fluid pressure which causes some hard shifs