The overdrive on a 1988 Toyota R22e pickup carrying a Winnebago does not work above 4000 feet altitude, according to the owners manual and my experience. How can I modify the pickup automatic transmission overdrive so that it works above 4000 feet altitude?

On long flat roads above 4000 feet, I have to keep speed 40-50 to not race the engine. Here the engine has plenty of power to run 60 mph without taxing either the engine or the transmission.

1988 4cyl toyota pickup 4x4 fuel pump fuses and or relays are located where

Perk, the fuel pump circuit opening relay is located behind the glove box. It should click every time the key is turned to start.
The EFI fuse is on the pass fender in the engine compartment. (hint, if the CEL comes on with key on, fuse good)
Calvin, try a new O2 sensor, a new efi temp sensor, and new thermostat. If you get it to a dealer, the Toyota fuel injector cleaner is a great product. It will help richen thoses injectors up some. The 22RE likes to run lean due to emissions. That's why the stumble @ idle.