2003 all road overheats at 75 degrees
When climbing hills. New thermostat
In Dec 2010, new coolant last mo, fans seem to work, use 5/40 amsoil,
Runs great in Seattle, overheats in desert (Palm Springs), car primarily used for long trips-not much town driving, new water pump and timing belt in Dec. 2010, car has 135K...
Any ideas other than a small fan on transmission?

If you haven't been using a 50/50 mixture of antifreeze and distilled water, mineral deposits may be blocking some passages in the radiator. An IR thermometer may help, but I suspect you need to replace the radiator. Be sure to fild the radiator in accordance with the procedure described in the Owner's Manual. This will help prevent air from forming in the cooling system. I would also use Amsoil Multi-Vehicle Synthetic ATF in the transmission, which will help it to run cooler and drop the temperature in the radiator.