I think we've hit paydirt, Keebler.
I installed the Trracer main spring, and the blending stopped. I have one of those hand held yellow radars; and I read 320fps for the first shot. The rest were in the 290fps range, with a couple spikes in the 300's.
Then I loaded a second mag, and was reading 250fps, with spikes in the 400's! I think I need a new battery. I was able to get through the second clip and 3 shots into a third (19 shots total) before velocity dropped off into the 220's. I'm hoping now that a regulator will help flatten and lengthen the shot count and speed.