Need advice/help 98 venture stalling

Hi, I just got done replacing the heads and gaskets, and the intake gaskets on this motor. It was hesitating so I cleaned the MAF and the hesitation instantly disappeared. But now it is stalling. If you keep your foot very slightly on the gas it doesn't do it. If you hit the gas and let off immediately, as soon as the RPM's are down to idle speed it will stall. It starts right back up though. Have any of you had this problem before? I checked the fuel pressure and that is right where it should be. It's also not the fuel filter. It has new plugs in it. I just wondered if anyone had this before and knows for sure what it is. Thanks a lot for any help.

It only does it when it's warmed up???

have you put a throttle position sensor on? also try cleaning the iac its right above the tps just don't scratch the bore of the iac or the tip alot of times it will get gunk built up in it. good luck