Get under the truck and you will find the TTVA - it’s a device that looks like a wiper motor. It is mounted vertical above the shift linkage and bolted to the side of the trans. It replaces the throttle pressure cable.

Have someone turn the ignition to run, but do not start it while you hold that TTVA. You should feel it energize.

Keep the key on for 60 seconds. The TTVA should go through a calibration procedure.

Shut the key off.

Then take it for s ride. See if that’s helps.

If the TTVA does not energize it may Ben stuck at wide open giving you late shifts.

You can remove the TTVA and take it for a ride - if it shifts earlier now, then that’s your problem.