1999 Chevy Silverado Engine codes P0174, P0171 and P0327

I have a 1999 chevy truck with a rebuilt engine 4.3L V6. Engine light coming on for awhile and then going off for awhile. The engine has about 3000 miles on the rebuilt engine. But I keep getting codes P0174, P0171, and P0327. The problem that I am having is that the engine light will come on for awhile and then it will turn itself off for awhile. Can''t figure out why. My cuz works at Firestone and he ran all the checks ( Smoke test, fuel pressure check). Cause there are no vacuum leaks, fuel pressure 59 to 60 psi, MAF sensor new, and the O2 sensors were changed last December. Like I said all these problems started after the engine was replaced and the reason it was replaced cause it spun a rear main bearing. Right before the motor went out I was pulling a boat with cruise control on, when I was approaching an overpass the motor raved up like it does with cruise control on, but when I got to the top of the overpass the motor didn't slow down like it should have so I had to stop it myself. An that's when the motor spun a rear main bearing. The repair shop said that gas got into my oil and caused the oil to thin out due to the fuel regulator going out. Any ideas? Will driving with the light on with these codes damage my motor?