Is he drag racing it and asking it to take WOT rips through the gears multiple times when its driven, or is it more of a cruiser? No doubt the Th400 is stronger, but unless you are beating on it the 2004R lives behind 455s pretty well. I have built both of them and if I have lots of power I like to use, it gets a th400, if it makes longer trips on the highway often, its gets an overdrive. The 65 is getting the 2004R, but the Formula has a th400, but then again when you have around 700hp/700tq a th400 is the least you can do. I've broken just as many Th400s as 2004Rs behind my engines, its all how it is used.