I think Colorado cars need to have the throttle lever bent, such that the throttle plate is held open a certain amount instead of closing completely. This to compensate for the thinner air up there.I’m the second owner and the car was purchased by the original owner in San Francisco at Herrera Buick in 1987.
If this has not been done on your car, that might explain why it seems to be running too rich.
I have two Hot Air throttle bodies buried away here somewhere, one from Denver and one from the East Coast. The one from Denver has the throttle lever bent as described, the one from the East Coast does not.
Hope this helps, as they say.