Had to replace the dist

Chevy express 3500 with 5700 vortex eng. The dist. Was replaced one time befor because the gear on the bottom was wore down so much it broke off two teeth. When I replaced it we had to put it on a pro. Scaner and rev the eng. To 4000 rpm and hold it for one minute so the pcm, cam sensor, and the crank sensor could relearn it self. This worked and I got better mpg(from 8mpg to 15mpg). Had to do the same thing when I had to pull the dist. To replace the intake man. Gasket and we did the same thing, it worked again(both times the check eng. Lite was on then we did test and it went out-codes told us ox. Sensor was bad but after relearning its self code went out. This time top of dist was broken loose from dist. Bottom gear showed wear, replaced it and no check eng. Lite came on but was still getting bad mpg(8)ran it with scanner on it like befor but this time no codes on and still getting bad mpg. Have learned 2001 5700 eng is kowned for dist. Problems, I think it is dist. Manuf. Proulbems. Any input will help