OK I HAVE A 97 GMC SIERRA 2500 4X4 WITH A 7.4 454 135K MILES NOW...

SO WITH NOT MUCH ENGINE GUY EXPERIENCE CAN SOMEONE TELL ME WHAT HAPPEND AND ALSO HOW TO MAKE THIS NOT HAPPEN AGAIN...

LONG STORY MADE SHORT...
DRIVING, TRUCK DIES, TOWED 300 MILES, ENGINE REMOVED, DISTRIB GEAR HAS BEEN SHEARED ALL THE WAY DOWN ON ONE SIDE, TIMING JUMPED 180 DEGREES, NEW TIMING CHAIN, NEW DIST,CAP, ROTOR, PLUGS,
ENGINE IS NOW STARTING AND RUNS LIKE YOU KNOW WHAT,,,
CHECKED CODES STILL OFF 42 DEGREES

ANY IDEAS COMMENTS WOULD REALLY BE HELPFUL
THANKS  

Did you replace the cam? The distributor gear on the cam is probably junk.

As for why it failed, I'd suspect an oiling problem. That's usually the cause.  

You sheared the dist. gear. Never saw that one. The cam must be junk, as it mates with dist. gear. Something must have locked up in the oil pump, since this is the only force the dist. would encounter. And you say timing is off 42deg.? Ret. or Adv. ? Did you do the repairs yourself?