FYI, my tranny temps and how they react are exactly like yours. I don't have nearly the weight nor the power you do. I had a small B&M cooler, which is a very good cooler, but decided to remove it. I wanted to be sure the tranny warmed up as quickly as possible. It did help to cool down on the highway, but still took a while. I did recently discover that the optimal operating temp for a transmission is about 190*. So, 200* really isn't that bad. I think running through the factory cooler is a good idea. The fluid should run thought the factory cooler last. The engine heats up faster than the tranny. So a hot radiator will help to heat the tranny up fast. With a 180* stat, tranny temp will try to remain around there. Most cars have a 195* stat, so a temp of 200-210 would be totally fine. If anyone is interested, I have the BIG B&M style cooler I would be willing to sell. It measures roughly 11x12x1.5 inches.
