1989 dodge ram 50 with Mitsubishi 2.6 dieseling

I know there are lots of threads on this topic. but none seam to be able to help with my problem.  I recently rebuilt my motor.  now running 135 lbs compression across the board. i am running a carter bbd 2 barrel  carb a pace setter header. ngk v power plugs.  one step hotter than stock. (the burn on the plugs looks pretty good if any thing a little on the lean side)    right now the timing is advanced as far as the distributor will allow. and i have managed to minimize the dieseling.   but still on occasion it will diesel.  I am currently running the distributor that has 2 stages of advance. but only have one stage hooked up. (the bottom stage)  to a port on the upper side of the carb that has vacuum when above idle but nothing at idle.  i do not know what rpm my idle is at but i know its pretty low.  ( ac pump all but kills the motor at idle)   I have tried to retard the timing and that only made it worse.   also i have eliminated all vacuum except the advance.  and running an electric fuel pump with about 4 psi pressure.  with no return on the carb to the tank.  I am currently getting about 22-23.5 mpg and thats running 75-80 on the freeway.  and 35 around town about a 50-50 split on a tank of highway and city driving.

 

so my questions are any suggestions on the dieseling issue.

2. what mpg does every one get.

3. if i were to add a return to the carb (drill and tap a port) would i want to regulate on the return side, or the inlet side and does the 2.5 psi every one has posted really work?