FWIK the transmission shifting is largely controlled by the PCM which decides when to shift based on throttle postion, RPM, and probably several other factors. I did notice on my V6 when my cats clogged up, that the tranny downshifted on the slightest climbs and would hold a gear longer before upshifting. This may have been due to the extra throttle I had give it because the engine had very low torque. If you seem to be loosing power, especially in the upper RPMs and it's more pronounced as the engine (exhaust) gets hotter, you may have a cat problem.
