Neither Fel-Pro or GM. Get aluminum ones like the set I got from WBS. Also replace the coolant elbows while you're at it if you haven't already.
Tapadatass
Most "mechanics" that don't know the 3.8 well say that but guranteed 99% it's the crappy plastic GM LIM gaskets gone for a ****!
Both the Fel pro and the GM revised gaskets are aluminum.