i had my engine rebuilt due to spinning a bearing, and every since I got it back it runs like crap. It will go for a week or two running good, then out of the blue I start it up and it barely runs. It starts fine, but then starts idling rough, then when you start driving, as you give it gas it starts bucking and stalling out, and backfiring. The MSD box LED light starts flashing real slow, and sometimes I lose the 4 cylinders on the LH side. I had the msd box checked it was ok, tried new coils,plugs,wires still no help. It has got to the point where I won't even drive it now. Does anyone have any ideas.Thanks in advance