Mark I was experiencing the same issue the last time I went to the Dragon, after I installed the 74mm TB.

The RPMs would go from sub 1,000 to nearly 4K and then back, over and over again like someone was revving the car. I never did figure out what happened, and I tore the entire intake/TB system apart several times with no changes. After I drove it a few hundred miles, it just started working properly and I have not had an issue since.

I was hoping mine was simply trying to adjust to having more air, but who knows. Have you changed anything recently? Added a CAI, TB, catch can?