I'm not a transmission expert by any means but your description sounds to me like you've got 1) a failing pump, not keeping the pressure up, or 2) a restriction that's affecting the pressure in or to your valve body. Do you have a shift kit in it, to firm up the shifts?

The way you seem to drive it, and wanting to consistently out perform your buddy if it were mine I'd either be looking for a good, local independent tranny guy to go through it and put in the right parts for higher horsepower use (ask the service managers at your Chevy/Ford/Chrysler-Dodge dealers who they use to rebuild for them); or shopping one of the known performance shops like Monster Transmissions for a replacement, ordered to fit your needs.

Just my ideas.