the driveshaft is being strained, you are running large tyres with a mean tread on them, if you can show us pics as to where the problem is, we could figure out what is causing the issue and what part can be swapped.
i broke my driveshafts twice on non-raptor cars because i ran large cooper stt's. imo, bfg's are better all around tyres... km2's are the best, the size of the tyres do matter as well.
do you really need 37's? the only reason id go for anything more than stock is if i were hitting the mud too often. to me, lighter rims, and smarter tyres (light and medium agressiveness.. aka stock ones) were always the better bet for gravel and sand offroading, i loved the grip with the km2's and cooper stt's... but they did take a toll on my driveshaft/rear diff, and i ran dana 60's both front and back. in 40k kilometers i broke a diff once, and the shaft twice. They didnt break overnight... but the nice thing was... i didn't go too big.. 33's ... so they didnt affect my warranty. mean grip also affects axles and diffs, not only driveshafts... so does towing... and so do heavier tyres.
either you go ahead and adjust your driveline, or go the stock route. increase in hp is awesome, but with that, you need to match it with a tougher driveline and transmission, otherwise you will run into probs... add to that ... larger tyres... well.. there you have it.
