360 mystery breakdown

Your engine sounds a lot like my367.It is 4.04 x 3.58, KB107s .005 out of the hole, .034 quench with a .039 gasket. 10.9Scr. Fresh cold air, and 205*F minimum running temperature. I have run three different cams in this with the ICA running 70*,61*, and now 64 or 66*. All on fat-boy bushed factory318 rods, with ARP bolts, and resized.
I run that FelPro1008 gasket. It's on it's third install. Good stuff. I also run ARP headbolts, lubed and IIRC somewhat over-torqued, on account of I was lazy and didn't want to go back and retorque it. I think I threw in 5 extra pounds.With Aluminum heads and with full timing and a modest timing curve I run 87E10. I've got over 100,000 miles on this engine now.I have had cylinder pressure as high as 185, but currently run 175. I am at 900ft
I tried the thin Orange gaskets when the pistons were a tic under the deck, but they were coming out by the end of the summer. I caught it just in time. I'm not sure where I purchased the Thin Orange ones; maybe Mopar? It mightabin the P4120094,IDK. In any case, I cannot recommend that Orange one.

I think she woulda survived with all-in at 3400 where I run mine. Plus I have a kink in my curve. I run 14* initial, 28* at 2800 and then it slows down to 32 at 3400. More timing didn't knock, but it didn't make her any faster either, so 32 it is. And 22* in the VCan, for 50* at 2800 for cruising. I have a manual transmission.

To run that high a cylinder pressure at 5000 ft takes a very early intake closing angle, or a very small total chamber volume.I know how mine ran with a 270/280/110 cam, at 900 ft. It was T-N-T. I bet yours is too. What stall and gear were you running? Iron heads?