Are you thinking of doing and engine swap, or buying a new blazer? For the cost of switching everything over it may not be cheaper in the long run, depending on the cost of the donor vehicle you can find. There have been some really nice worked over subs and blazers poping up lately that can be had for well under 10,000 dollars. a truck with 3.73's, 33" tires, and a 700r4 or 4l60 should allow you to pull down around 20+ mpg cruising on the highway(hypothetical using rpm, speed and the design parimeters of the 6.2 engine). Hope it helps.
Cheers, rugger