many people have gotten 300,000 miles out of the transmission.. as they run much much cooler 150-160F when it's 100f outside i have never seen it go above 165F even hauling-ass uphill .... but i do typically SPEED up on the down hill side and let off the throttle when it reaches the next up hill
my transmission has 110K now it's still STRONG fluid is clean still it has never been serviced besides the replacement Aux pump..( as they normally start getting weak around 100k miles)
internally it's nearly identical to a 4L60E so fixing it should be pretty easy...
also taking into consideration that the transmission is barely rotating at 1,000 rpm at 40mph and 2200rpm at 85mph on flat land ..typical acceleration is 1,000-1300rpm... while a typical 4l60 will be rotating at 3-4,000 rpm for extended periods on long hauls
you can always get a used one from a wreaked one. make sure the AUX pump gets replaced though..and a oil change and new two new filters