Actually it's been doing great now that I started keeping it out of overdrive on the hills while towing. No more transmission codes and it shifts nice and strong. The only issue I have with the truck at all is the occasional overboost code still.
My general contractor on my house build has the exact same truck, only with an 8.1 instead. They were parked next to each other the other day and I asked him how many miles it had on it and he says, "well, it's getting up there a bit. I've got about 90,000 on it now. What about you?" When I told him I had 364,000 miles the look on his face was priceless.