A few days ago we took my wife's 4Runner on the 3 hour trip to the Lake of the Ozarks. The trip from Kansas City is full of long, minor inclines as well as steeper short hills. Speeds ranged from 60mph to 80mph. Just prior to the trip, I convinced my wife to uninstall the TRD exhaust and put on the stock exhaust back on because the kids and myself were getting headaches from the all the drone that exhaust creates under almost any load. We had the TRD exhaust installed for 1 year.
Obviously, the trip was FAR FAR FAR more enjoyable with the major reduction in drone. My biggest surprise though was that the truck NEVER once gear hunted. The throttle response also felt a bit better and the transmission would do unlocking of the torque converter in 5th as opposed to almost always shifting into 4th. Even more surprising was the MPGs. We saw nearly 20mpg for the trip including running through 15mph cross and headwinds and a paddle board strapped to the top.
I think the 4.0 V6 and transmission ECU are not happy with the higher flowing TRD exhaust given that it's annoying shifting behaviors were significantly reduced with the install of the stock exhaust.