I'm thinking crud in the metering block or throttle body. I'm not the first one to find this problem and probably won't the last, and I've seen a few members here have this problem with the Avengers too. It sucks and shouldn't have to be done, but there it is.
Btw, you should have seen the milling swerlies I pulled out of my Crane rocker shafts, lol. No excuse for this as the rocker arm/shaft kit was 300+ bucks. Damn glad I checked.