Are you using a boost control selenoid? If youre running off of just the wastegate spring, this may be some of the issue, as the boost control selenoid allows complete control, and has shown to eliminate boost creep in some of my previous setups.
You might want to pull the wastegate off, pull the WG top off and make sure the diaphram is not pinched. I have had wastegates directly from TiAL that had pinched diaphrams. Check this out, as it sounds like it could be a culprit.

 

Thanks for the advice Spoolin I will keep it mind.

Cody, you're alive! I'll give you a call.