The 47 can't handle stock HP ratings let alone anything more. And don't for a minuet think the 48 is any better. The truth is, even it you don't want to hear it, the auto in it's stock factory trim started deteriorating the first mile driven. That rate of wear, is directly proportional to HP, use, abuse, maintenance and torque. The harder you work it, stock or modified, the faster the rate of wear. If you are the guy that is always in the slow lane, never tows, watches his maintenance, and uses a light foot, you will see a long life. But, at some point it will fail. This guy might go 100,000 trouble free miles, maybe more? Who knows? But at the same time, every jack rabbit start, heavy tow, or large payload you haul, reduces the life Span of your transmission. There are no free rides with transmissions, you abuse it you lose it. The better it is treated the longer it lives, this is true with all transmissions, stock or modified. The only difference is the modified trany's have a slower wear rate, how much slow? Depends on you. Heat is the killer to the automatic, for every 10 degrees over 190 degrees, the life span of ATF is cut in half. So if you thought you could go 40,000 miles between changes, hit 200 degrees and the ATF's life is now 20,000miles. Hit 210 and we are down to 10,000, 220= 5,000. All this heat comes from friction, more load equals more friction which equals more heat. The best thing to ever happen for the automatic is synthetic fluid. It can withstand the higher heat, and does not break-down like non-synthetic oils. But even with it's use, the auto will still continue to lose life with every use, just at a different rate. Same goes for the manual trany, with every take off the clutch wears. Ever see some idiot next to you at a red light, and he keeps using the clutch to hold the truck? Back and forth, back and forth, this guy wears his clutch more at that one stop then most would at 15, maybe more. His clutch wears like everyone else's, only difference is he replaces his once every 2-3 years and others might go 5-6 years. His rate of wear is accelerated, by his actions. No different then the automatic guy.