The trans will be the weak link. There are things many do to the stock trans, Valve body, cooler, One of the most important things for towing, MAKE sure it has a good cooler, remove the STOCK one and install a 6oh cooler. Much larger tubes, many more than stock. It will keep the life blood of your trans much cooler. It bolts right up into the stock location, and has minimal pluming changes required. Easy add on for sure. If he has ANY doubts about his trans. Call Brian down at BTS in Arkansas, Brians Truck Shop
he will NOT try to sell your brother a new trans. He will coach him on what to do and not do to try to increase the chances of the stock one surviving for as long as possible.
If/WHEN he needs a new one, the BTS is HIGHLY reccommended among the PSD community. (Since your in the central US area anyway.) Probably only 12 hrs or so away, depending on where you are in Mi. The trip there is well worth it when you get one.