3.73 vs. 4.30 AXLE RATIO

We towed our old FW, 1993 Jayco Eagle 215SD and various boats weighing up to 5,000# starting with a 1987 Chevy 3/4 ton 350 with 4.10 gearing up to the 2003 GMC crew-cab D/A combo with 3.73 gearing. Got rid of the old 350 after one year of lack of power and real low gas mileage. Then went with two different 454s, old one and a newer Vortec one and 4.10 rear ends and they both pulled our loads fine with pretty poor gas mileage when towing both FW and boat, about 8 mpg. Stepped up to the GMC D/A combo crew-cab in 2003 and what a difference, about 50% better towing our outfits, around 12 mpg and a 40% improvement in town, unloaded. Now, we pull with a GMC D/A combo crew-cab with 3.73 gearing and a little larger FW, a Jayco HT 26.5 RLS with a total weight capacity of 9,950, which I don't believe we will ever achieve and a 4,000 pound boat and trailer. We still get around 12 mpg pulling our outfits and, when buying our last truck 1 1/2 years ago, I thought about a gasser, but really liked the diesel for its power and mileage. I don't think that, overall, the maintenance costs of a diesel are significantly greater than with a gasser, especially if you opt for longer oil change intervals using synthetics. Hope to keep this truck for as long as the first diesel, over 100,000 miles. With the new transmissions in these diesels nowadays, I'm thinking the 3.73 is the optimum gearings rather than having to go to 4.10.