Trust Boost Gauge, or Boondocker Boost Sensor?

i think you might have a bad boost gauge or something a long the lines of a bad T fitting or some restriction in the lines, my boost gauge is spot on to what my BD box says my max boost is every time.

and to answer your question i would trust the BD box over the boost gauge

Sounds like the notorious boost spikes of the boost controllers. Have you removed the spring and ball from the boost controller?

I had issues with my Boondockers box registering a high PSI with only 6psi being run. Took the ball/spring out and now my box reads only 6psi max. Unless I crank up the knob of course.

Go to turbosmart's website and look for the boost controller instructions. It will tell you how to remove them to cure the boost spike readings.