boost cut or fuel cut??..whats wrong :(
 

I have an '88 13bt manual, with a series 5 engine, tranny and drive line a 2 1/2" exhaust and an HKS intake, I know my factory boost guage is stuffed becasue it only goes up half way on the guage, so I got an Autometer boost guage. I can boost up to 9 or 10psi with this but it cuts out, is this a boost cut or fuel cut?? I know it should only be boosting about 7psi but with the exhaust and intake mods would it be enough for the boost to creep up to 10?? the car kinda farts when boosting high all other times its sweet as. It accelerates hard but gives about 2 seconds of pulling power then a second of * faaaarrt * noise and looses all power, then power comes back again for 2 seconds...untill i let it off boost. Also while i was doing this last night when i let the boost off the guage went all the way to 15psi then back down??