Setting Idle speed / Stallingin gear

OK, without making my self sound like a complete idiot, here i go....

I have a holley carb, not sure of its size or model.. the only numbers i can find are anywere are p-80 and 11716.. Oh yeh, its a 4bbl with elec choke and vacume secondaries.,

I have not found any vacume leaks anywere.
The i may be wrong, but i dont think the timing is the issue becuase it will idle fine in park or neutral, but I will be glad to check that out tommorw (in another 5 degree day).
This car came from Colorado so I think it may be leaned out.. but I am not sure why it will idle but not in gear. I am not the brightest when it comes to carbs, but I am learning fast. I am not sure how to test to see if it is running lean or rich. I am sorry, i probably sound like a noob here, but trust my I know what I am doing, just not on carbs.

Thanks for the tips, and instructions would be great. The guy i bought it from drove it all the time before I bought it and had it shipped here, but I cant fathom that altitude change would cause it idle out of gear and stall in gear. Unless of course, the guy was lieing..