loose/disconnected/cut/cracked/improperly connected in your wastegate actuation system and its letting pressure bleed from somewhere. That will also account for your wavering boost level. Sounds like you need to go through it and find that problem.. With the .035" jets you will have veyr stable boost at 14-15psi. I put an ECU in a 95 with 40,000 miles and .035" jets were installed. Boost came up to 15psi, stayed nice and level and dropped to 13-14psi around 6500RPM. This car is in great mechanical shape so I dont suspect that there are any leaks in the wastegate system and it was working correctly.
Check through it - I'm sure you'll find something..