Sounds like you've burned some of the bands - an automatic's equivalent of clutches.
You may be low on fluid, or just pushing it really hard. Either way, it's almost time for a fluid/filter change anyway, and with severe use, I'd up the schedule.
Porsche claims it's a lifetime fluid... but the manufacturer of the box (ZF Getrieb) recommends a fluid/filter swap every 45k mi. Audi, BMW and Jaguar all used the same box - ZF 5HP and all used to claim a lifetime fluid. All have now changed to the 45k mi. service interval. Be sure to use only ESSO LT 71141 fluid. While some fluids claim compatibility, ZF says thay've had issues with boxes using other than the ESSO fluid, and they're pretty emphatic about only using LT 71141.
Threaded Mode
