I just drive the snot out of my cars. I figure if I break something I'll fix it. I've got over a million miles on the two diesels and 2 gas cars I'm driving and I've never rebuilt a transmission. We have a 5-speed in a turbo diesel ... 2nd is good for a max of 40 mph. My wife was driving and heading up a 7000 ft climb outside LA and I suggested she down shift form 5th to 4th. She downshifted from from 5th to 2nd (missed the gate) and at 60 mph laid a patch as the rear wheels slowed. 200,000 miles have passed and the tranny still doesn't show any ill effect.