Just bought a 77 D-100 with a 440. The seller installed a new TM-7 intake and carb before I bought it. The problem I'm having is that after it warms up, it doesn't want to stay running. It keeps dropping cylinders until I bring the rpm's up. I noticed that he installed the aluminum intake using the stock valley pan intake gasket and nothing else. I'm thinking it should have had the Fel-Pro 1216 composite gaskets installed to sandwich the stock intake gasket. Wondering if that could be causing a nasty vacuum leak around the intake manifold?
Anyone ever encountered this?

I use the stock pan with my Team G with no problems. I think if he did not change the pan out when he put the intake on that could be the problem. Have you cranked it up and let it run and sprayed wd40 around the intake to see if it changed rpm? Easy way to tell if it is leaking or not.

If he did not change the pan out it would have been crushed around the ports and could cause this.. The pan down here at auto-zone is $20.

yes,mine did this after transplanting it from a MH to the 88 truck.

i used the felpro vallypan that has the heat crossover blocked,it came with 4 thin paper gaskets. 1 for each side of the tin pan.

i put it on dry and have had no problems. runs like a new engine compaired to how it ran with a vac leak.

IIRC it was a felpro 1215HP valley pan.

I'd pull the manifold and make sure it's machined straight to start with I've seen plenty of manifolds cut crooked.

No matter what you use for gaskets it won't seal with a manifold that doesn't mate properly with the heads.