Mine does the same thing. I first noticed it on my cross country drive, when my hand felt warmth from above the e-brake. I investigated and found that the bolts holding the seats were very warm. After that drive I really only notice it on either hills, or drives of over 45 minutes. Its a little disconcerting, given the reputation that our transmissions have as being heat sensitive.

I changed my transmission fluid to mobile 1 ATF, and the heat issues were delayed a bit when driving. The fluid that I took out was unfortunately still very red and looked moderately clean. I say unfortunately because it would have been nice to have had a culprit.

I have been having some antifreeze leakage. I know that the transmission cooler lines go through the lower part of the radiator. Given the VXs penchant for overheating on a hot day, this problem may arise do to a degradation of the radiator's cooling capabilities over time.

It would be nice for everyone with this symptom to to list the miles on your car/radiator and transmission I have ~99,000 miles on both the engine/radiatior (and I believe the radiator has never been changed) and the transmission. The radiator was removed two months before my cross country trip to replace a busted waterpump and timing belt by the local acura/isuzu/subaru dealership. This repair has not solved my coolant leakage problems.