All of the suggestions that bigmoose provides make sense and should be checked. Excessive endshake can result in misfires. The best remedy for endshake is either to stretch the yoke tube (gunsmith) or install proper thickness cylinder shim bearings; either of which provides the same end result. I have used the shim bearings on several occasions and they work very well. One thing to note is to also check for yoke endplay with the cylinder removed and yoke in place. Correct yoke end play first with yoke bearing, then address cylinder endshake with cylinder bearing.