Which u-joints you use are a factor as well. Solid Spicer u-joints have worked flawlessly for me in race applications. They must use very good grease since they don't have grease fittings (which weaken the u-joint because of the fitting as well as the cross-drilling). Cap mounted grease fittings are likely stronger than the ones in the u-joint body. Even in mild applications with the best brand u-joints, a u-joint with a body-mounted fitting should be installed with the fitting area being in compression as the drivetrain rotates. It's the weakest link in the "chain" that will usually get ya!