Mine is a little loose too. My vibration I swore was the LH front tire. I put new tires on it and same little vibration. I put pinion shims on top of the springs to raise it a little and like you no change. I tried lowering the angle and it didn't like it at all. I just chalked it up to a worn trans and I'll live with it. It's not a bad vibration but it is just annoying.

Mike, I got sent to a spicer class years ago and they flat out stated that a u joint with a zero operating angle will fail faster than one that doesn't get greased regularly. I found that very surprising but they obviously know what they're doing.