Magnum and Wiring Swap

Well, I replaced the MAP sensor and set out to put some miles on the car. On the initial test drive in the neighborhood, it fumbled and backfired a bit then cleared up. It started running better so I decided to go further. My wife and I (because breakdowns are more fun with company) drove it around 100 miles or so yesterday and it seemed to run pretty good. The CEL came on a few times, I assumed for the missing VSS. I'll run the self diagnostic and confirm later.
The only weirdness I noticed is that after filling the gas tank, it started fumbling at low RPM loads during acceleration. My guess is that how I have the EVAP system hooked up is causing it. I'm using the Tanks, Inc. EFI conversion tank with their new fuel lines and a GM returnless filter/pressure regulator. The tank has an external vent/roll over valve positioned above the filler neck.