Are you positive that you put the adaptor, donut, and 3" gasket in the right order at the DP-to-CBE connection?
You should have a normal 2-bolt (3") gasket up next to the DP, then the adaptor with the protrusion facing towards the rear of the car, and the donut gasket with the tapered end towards the rear of the car. Just trying to make sure here.
If that's the case, tighten the shit out of that connection just to rule it out for sure before you do everything else. Tighten each bolt a little bit at a time.