I thought about the 50 degree thing. That could very well be it, but don't a lot of the guys running Spidertrax junk turn 50 degrees with u-joints? I wouldn't think the actual brand/type of the joint would matter as long as the shafts are clearanced properly. Considering it's both sides it's most likely not a buggered shaft. I think your best bet at this point is to try some stock joints and just see what happens. Run some straight line stuff, then run some stuff at full lock or close to it with a lot of throttle. See what your results are. Either way it takes a lot to push out a tacked in cap. Before I went to CVs I tacked my caps in and never had an issue. How much power are you running?