the car boosts well up to 16 psi builds and then when i change and carry on it falls rite back down to -15boost whats up with it?? could it need a new -31?? or anything else u can fink off?

doing me head in also the cars fitted with a paceintercooler,induction kit 195 chip and been adjusted to 16 psi.

it boosts gets to 15 almost instantly feels slow then holds back and doesnt get any quicker till ya change gear as if its holding back or summing ??

anyhelp lads would be sweet