that it i have had it with the boost problem

[Clarky]

Had the same problem, changed the check valve under the pressure tank as you say, and all fixed.
 
 

If you are still on the standard ecu its very likely boost creep and you ecu retarding the timing, i had the same problem till i switched to a pfc. If your already on a pfc then ill go with a check valve probably the one under the pressure tank.

[stronzen]

which pressure tank do you mean ? where is that one located :-) ?

[neil_jdmr]

Its just in front of the uim and behind the alternator