I have Grantshire's M715 sitting here now with the 6.2L in it that Spicergear built several years back. The 6.2 does the job fine in that truck and I just swapped the axles for a Dana 60 and 14 bolt combo with 5.13's and 42" tires.
After I am finished with his truck, I am planning a 6.2 in my 715 with 4.56 gears and a 205 with my 38" Michelins. Like you said, it will suit my needs fine, and certainly get better than the 5 MPG I get with my 396 Chevy now. Keep the 6.2 in its original design limitations and it will do a fine job hauling your truck around.
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