Stock gti with s3 intercooler pressure drop ?

[jhook661]

I have a stock gti with Revo intake pipe
 I fitted a boost gauge the other day my turbo spikes at 10-11psi then drops between 7-3psi redline tempreture depending  maybe a boost leak ?! I looked underneath my car as well and looked at the intercooler pipes and it has jubalie clips to the intercooler could it be the s3 intercooler would that make my turbo pressure drop ?