I had my motor rebuilt from a very well known engine builder in my area. I got the engine put back in at replaced everything back but with all brand new parts either ac Delco or Dorman parts. My issue I'm having is it runs like crap spitting, sputtering, and backfiring but once circuits close runs great just a slight miss can be felt. Spent 2 days adjusting the distributor was watching the spark advance on the scan tool was reading -25 to -30 no matter what we did wouldn't change. Found out that after each adjustment you have to shut the engine off then restart won't read live and started seeing results but could only get it down to -13. I was told by a mechanic that the spark advance on the scan tool is the timing and not sure if that's true because first it new to me second when we finally did get it down to 0 to -1.5 truck runs even worse. I have researched and can't find any info if it's timing or where the piston fires because if it is firing position means they are now firing pretty much top dead center and I know that's not good for the motor will bust the pistons. I guess my main concern is the spark advance being set at 0 now where should it be set at and I'm putting it in the shop Friday to get it straightened out after 6 months and lots of money I'm exhausted but just worried about driving it to the shop now. Do I need to adjust the distributor back or forward more. My scan tool doesn't read cam shaft position ordered one but hasn't arrived yet. Any help would be great appreciated going insane.