Mapp sensor problem

[mike2]

Having a prob with a 96 model 305 vortec rebuild. It seems to have us stumped.
Problem: On a fresh rebuild, a comp cam(basically the same cam as a GM RV cam) was installed. This being a roller motor we felt all things would be equal. Not so. Just the little difference in the cam caused a loss of vacume. The reading is 15 lbs and it should be 18-20. The mapp sensor reads this and richens the mixture. Thus, fuel mileage and performance goes down the tube.
Has anyone had this problem and what was solution, short of burning another chip and reprogramming computer.
Can a vacume booster be installed and will it do the job?
Help