Well, I moved the source to the center port, and saw a 1psi swing. But, it was also Td off with 2 other devices (FPR & CBV). Now, I have my MAP by it's self. I just need to log it's values again. I expect to see little to no swing. Even the stock MAP sensor swings just a little.
Also, the 2-8 psi was the max oscillation. The average was more like 3-6. But, that's still a 3psi change, and resulted in a 3 deg difference in timing.
Now, at least it's only a 1 deg affect, and hopefully less.