Standard boost levels:
Gears 1-2 0.54 bar
Gears 3-5 0.72 bar
Base boost 0.40 +/- 0.03 bar
Pressure switch cut-off 1.15 bar
1 bar = 14.7 psi, you do the math.
When you install a MBC, you should be getting the same boost in all gears, it bypasses the operation of the solenoid valve.
By the sound of it, your MBC is not doing what it should, the ECU is still controlling boost through the solenoid valve.
you may want to check the plumbing, and/or set up the MBC properly.