It would be interesting on how the intake sit's down on the heads and block without any gaskets. This may show if the heads were milled or if the manifold has a warp to it.
The next time you have it apart set the intake down and if it hits the block first, the heads were milled.
By all rights it should fit almost metal to metal without the gaskets on all surface's.
This may show that there is a different sealing problem.
I haven't gone back and read if the heads and intake are new.
After you pulled the intake off, were there any witness marks on the gasket's as to squashing in a spot where they shouldn't and do the gasket's match up to the intake and the heads. If they were ported any maybe you have to go up on number for sealing, just a thought.
If you have a wide mill file try running it across for flatness on the intake.
What Wheels427 said about ONLY using some silicone for a gasket will work. Permatex makes a black & a blue oil resistant silicone that works very good, BUT must have a good day of curing time before its started. Wipe off the squash with a good putty knife,then a wet rag. Water help's the curing faster.
Are you using the gaskets that have a pronto seal on them? They seem to work better. I would recommend going to a #20 torque and after it sets up re-torque to 25#s and try it out.
Luv the smell of NITRO in the morning.