Bypass valve stuck open?

88 Turbobird just diedish. Out of nowhere it wouldn't rev above 2k or under boost and it sounds like all of the boost is being dumped (hissing) being a diesel guy I have had this problem on navstar motors and it would usually be a bypass valve being stuck. I haven't been able to trace any obvious boost leaks yet (cracked lines etc,..) and it dumps a sh*&load of fuel while this is happening. Runs great off idle tho lol. Anybody else ever have a similar problem?

What bypass valve do you have on it? They don't have one from the factory. Boost leak maybe?

All stock. must be a boost leak then.

Turbo to intercooler hose split wide open.