Another common cause of thrust bearing failure is the finish of the thrust surface after crank grinding. The grinding wheel will leave hatch marks that look and act like a saw blade. Look closely at a reground crank and you will see what I mean. Most crank grinders will touch the thrust surface with the wheel to verify trueness. When they do this it leaves the "saw blade" on the thrust surface. You really NEED to hand polish the surface with 600, then 1500 grit paper. This has decreased my thrust bearing issues to almost nothing.
Yeah, its pronounces "thrust", meaning linear movement along the rotating axis...in and out, front to rear. If the engine builder doesnt properly crush the bearing prior to final assembly, this will create a lack of clearance that ends up being worn out, and once wear begins, it doesnt stop, because of the resulting surface finish and it's rubbing on the bearing. Once that happens, the crank needs to be re-ground. All it takes is to bolt the crank in, with the bearings installed (obviously), oiled, and the caps torqued down. Then using a big chunk of brass and a big hammer, smack the rear of the crank and the front of the crank snout (straight, not sideways, lol!)...obviously using the brass piece as a punch. Smack it a few times on both ends, then use a long screwdriver to pry the crank forward, set your dial indicator, then pry the crank in the other direction to check your clearance. This creates the initial crush.
If you bolt your tranny up, and start bolting up the torque converter, you should have somewhat of a gap. Mine was about .100". If you dont have a gap at all, start looking for cracks in the bell housing because you may have forced the engine and tranny together with the bolts, without the TC being fully seated. I saw some kid do it when I was in high school auto shop. He blamed it on the wrong flexplate, even though it was the same flexplate and TC that came out of it.