5.7 vortec in 72 c10 issues

[lanehicks76]

Hi guys. This is my first post, but I have been reading through this site for some time now. I recently bought a roller 72 c10 long bed. I had a 98 5.7 vortec from a truck that I put comp cams magnum 280, comp cams bee hive springs with required hardware, aluminum dual plane intake, holley 750 vacuum secondaries, hooker super comp 1 7/8 headers and jegs quite flow fuel pump. I installed cam straight up as per comps tech line. IM having trouble with backfiring through carb and exhaust. It acted like the valves were to tight, but I just ran them again to zero lash plus 1/4 turn. Also I have played with timing and all the same. Has anyone had this popping, backfiring issue. Thanks in advance . Oh yeah all parts are new and the long block was running strong before it was pulled.