Hopping is what kills them, or like what Wanna said, not applying power smoothly. There is a guy with a 4bt in a ranger that is running something like 600-700 hp IIRC, and he is running a stock ranger rear end. Don't beat the crap out of it. It will hold up. Mine was rebuilt once at 350,000 miles. It was WORN out though. It didn't just blow up. My truck was used to pull a fifth wheel trailer full of mineral at the time. It did go off road, and did get beat a little, but not excessively.

 

Always that surprises me you aint broke it. Im close to 400 hp and my 70 is still fine, i dont baby it either.