Sounds like you got the idle circuit set up good. The main airbleeds add air to the fuel when the main circuit is in use. So that means all cruise and heavy accel, WOT etc. The air from the air bleeds mix with the fuel and form an "emulsion" (just like mixing up some oil and vinegar for your salad) its kind of a frothy mix and this in turn mixes with the incoming air stream, the mix is pulled out if the orifice in the middle of the center venturi booster (dual round horn shape things, one inside the other) now, in the late 70's and on, the emissions were getting tighter and tighter. GM decided to try large main airbleeds to form a more consistent emulsion, great but just one problem, they're not as "responsive" when it comes to performance. Note that a lot of chevy trucks came with these where outright performance was not as much of an issue. Also notice that larger jets were used with this and some appropriate rods to get the fuel curve in line. Much testing was done and on a completely stock truck etc., this worked ok. going to a smaller airbleed returns to the earlier setup where the rod and jet choice is not as "touchy" of a choice. So, in reference to your set-up, I think if you "shrunk down' the main airbleeds, it would be easier to tune the main circuit. I believe in recipe one would have a good starting point as far as size.
Also, remember, that at your elevation, you can get away with more timing. Like if you are at 36 degrees total, you could probly bump that up to 38. You have less air up there and so the engine has less cylinder pressure. It like lowering the compression ratio at that altitude. IIRC, for every 2500 feet in elevation, you can go 1 more degree of timing, and that is every where on the timing, idle cruise etc. Might be something to experiment with.
