The bottom end is fairly bullet-proof, but that only includes the crankshaft, bearings, rods and pistons. The wear is faster in the cylinder bores and rings - mostly cylinder bores.

I'm real curious about the other thread and the change when the fuel return line is pinched..... pay real close attention to what Eddy said.... he's absolutely correct. If I had experienced your problem and found that it disappeared when the return line was pinched, I'd first replace the fuel filter and see if it fixed the problem.... if not, I'd check the voltage at the fuel pump. If that was ok, I'd replace the fuel pump AND the FPR - just because I'd be damned tired of fooling with it and I would have confidence that there was a pony in the pile of parts.

Frank