2009 cobalt lnf was just building boost just fine and all of a sudden go to give it gas wont go past 1-3psi. Zzp intercooler kit, dp. And a tune. Any ideas?

 

Just as a general starting point on any turbocharged car that suddenly stopped building boost, check all the charge pipes, hoses and clamps from the outlet of the turbo compressor all the way to the throttle body and see if something cracked, came loose or popped off.

If you're sure everything is good, pulling the inlet tube off the turbo and make sure the compressor wheel spins freely. If there was a problem with the vacuum line(s) affecting the wastegate actuator, you'd either get max boost or minimum boost the spring tension will provide, which should be more than what you're seeing.