So, try this: Run a length of hose directly from the turbo`s compressor housing discharge nipple to the WGA nipple. Adjust boost by rotating the turnbuckle on the threaded end of the adjustable length actuator rod. Rotate the turnbuckle in, clockwise, which effectively shortens the overall length of the actuator rod and increases WG spring pressure. Try about three coplete 360* rotations to start with.

 

Wait....you have only 14.8 psi boost...when you let off the gas RPM drop to 200...your mechanic told you the rpm drop was normal? Find a new mechanic ! Wastegate boost is around 11 psi +/- a couple psi. This sound like a simple vacuum leak. Keep in mind it does not have to be on the wastgate or turbo to effect this, you have to check all vacuum lines.