Feel like 360 should have more power
I could add on to a bunch of what everyone else is saying to modify the engine with but until the tune is confirmed to be good there's not much point. 100-110 psi cranking sounds about right for a stock-compression 360 LA with a mild cam at that altitude. I lived in CO for 15 years, the thin air is a real killer for NA engines.
Make sure that thing has a bunch of initial timing, like 16° minimum, maybe even 20°. Total (not including vacuum advance) around 36°.