That A518 is tough....I'd put it up against ANY of the RH's or RE's anyday. I put a crap load of BD stuff in my 92...HP pump, injectors, turbo...etc.,etc. Only problems I ever had was high EGT's from all the fuel....Trans worked flawlessly for as long as I owned it. A much bigger trans cooler is obviously the ticket....keep it cool. The biggest problem with those old trucks is the smallish radiator. If you could get something even 20% bigger, it would make a HUGE difference.
And then there's the "NUT" behind the wheel.....common sense when under full boost will go a long way as far as longetivity.