Hopefully someone can help out. getting a vibration it seems like at idle, and it goes away at higher rpms. was thinking it was the exhaust the way the boat sits in the water and the swim steps above the tips. I have heard that the engine would have to be pulled out to replace the u joints, how hard would that be?

Check to see if there is a lot of slop in the splines of the drive line and pump shaft.  Try rotating the pump shaft back and forth through the hand hole cover or through the intake.