I may have missed something, but is it backfiring at all? It looks like it is missing or un even compression from the video. I have never ran adjustable rockers on a MOPAR, but had a small block Chevy in the past. I once over ajusted the valves, and it ran crappy. I am thinking because the valve timing essentially gets "slowed down" for lack of a better word. the cam is pushing againgt tighter resisitance, and who knows if the valves are truly closing completely. Did you try adjusting the valves running? It can be messy, but if its hydraulic lifters, back the rocker nut off till it starts tapping, then run them down till it stops, plus another 1/4 to 1/2 turn. If you static adjusted them, you may want to try a "engine running valve adjustment". If it is solid lifters, you need to set valve lash with feeler gauges. I know setting the valves running is an oily mess, what I used to do is make a shield out of tin foil, and set it over the oil holes on the rockers. You can bed the foil to stay in place and still access the bolts. You may be doubting this adjustment, but if you know what you are doing, it is pretty quick and painless. its worth a try. Like said, I have been there and done that with my SB Chevy, it happens. one more thing Id like to point out, if your cam is mild and not that lopey, your vacuum reading is 5-8 in hg too low, I'm thinking 15-18 in hg, should be coming up on that guage.