If I'm driving normally and just go 1/4 boost or 1/2 boost which is between anywhere from 8-14psi I have no issue. Now if I get into the red or 15-21psi my car starts to hesitate and the boost drops down to 5psi and then back up to 15-21psi and then back down and up and so on. I've checked for leaks in the intercooler and hoses. I noticed a flutter on the air intake side when I let off the gas. I checked the tension in the wastegate and it seems nice and tight. I do have a smbc setup but it never gave me trouble in the past. What should be causing this issue?