Man, what a shame they didn't pass it down to you - that is a sweat looking GMC! I was told at the show my truck would likely go for in the low 30s. So almost even in what I have in her :-)
As for gas MPG - I am doing pretty good for this old V8 ran on its proper Quadrajet 4 Barrel Carburetor.... 14 MPG on my trip up and back from Kilgore (~600 miles round trip). I have a way cool
progression distributor. On the fly timing adjustments and distributor lockout (no start) controlled by my iPhone or iPad. From the outside it looks like a stock distributor. But it cost a sh*t ton of $$$ too.
As for Broncos .... I could only wish for one of those (or a K5 Blazer around my year model).