OK, my car now screams & I'm quite pleased with it after having it down for a month. In 3rd gear the boost will hit 10psi. With the throttle floored, at around 5800 rpm or so, the boost drops off to 5-6 psi. I have no idea why. Feels strong, no power drop, POS AutoMeter boost gauge. Any ideas??

 

i'm getting a simlar situation.
except mine started off with boost creep???
what is your downpipe like. standard one is crap. when the wastegate opens, the exhaust gas runs into a big fat piece of metal (3/4inch thick of iron with opening size of turbine) and then creates turbulance with the exhaust gas comming out of the turbine. with the post 89 rx7s this tends cause boost drop off towards the top-end. with the pre-89 it tends to do the opposite.

what u should have is seperate pipes comming out of both the wastegate and the exhaust turbine which later join up flowing in the same direction (sort of like a entrance to a freeway). or u could have a seperate exhaust pipe comming off the wastegate which goes straight to the ground and makes a big raw rota noise when opened (like some of the big turbo dudes with external wastegates)