You could be right. I can tell you this though, I don't think anything bigger than a 32" tire would fit without a lift kit. We had to adjust the front torsion bars to lift the front the way it was and the tires still slighly rub when turning sharp in reverse.

For a stocker pulling medium loads, under 10K, my opinion is a 3.73 is enough gear. Especially for someone that doesn't tow much. I know his boat weighs 11,500 but 1000 miles yr is nothing.

I agree with you on pulling under 10,000lbs and a tire under 32". On my 02 1500 HD I have 285 75R 16's and they do slightly rub when backing up and turning sharp. I have my torsion bar cranked about half way. Your wider tires probably make a difference for the shorter height than mine.

I had an 01 2500HD with the 8.1 and allison tranny, with 285/75/16 tires on it. The truck pulled really well however I thought that 3rd was a littles too low for the motor and rearend ratio. There was a particular hill, quite steep, I pulled my 6000 lb package up wvery other weekend, and it wouldn't pull the hill in 4th and revved the heck out of the motor in third. Passengers always commented, You going to blow it up aren't you, my response, It was built to take it and it's under warranty. Tough truck, terrible mileage on mine, 7-7.5 for every day driving with 11-12 highway and 6-7 towing. I was ready to buy stock in BP before I traded it. Really considering technology today I thought the truck would do somewhat better on fuel without towing than it did. I understand the tires hurt the mileage, but a buddy has the same truck still with 265/75/16 and his mileage is no better. I will say with the bigger tires the ride was really nice. I probably should have put a programmer to it and took out the torque mgt, I understand that is what holds them down in 1st gear from blowing the tires off the rims. Go 4.10's and program the truck for performance, another half or whole mile to the gallon isn't that important. I have an 04 SS with the 6.0 and I love that package, for towing my 6000 lb package this year.

I'm really surprised you thought there was that much difference between 3rd and OD. I've never heard anyone say that they felt they were pulling too much RPM in 3rd then not enough in OD at the same speed. The ratios are fairly close together. I used the Hypertech programmer on my 6.0 liter and feel it was a good investment because of the ability to change the shift points to where I want. One thing for sure is that motor likes to run more RPM than Fords or Dodges. I get 14-15 on the highway and 8-10 consistantly pulling 7000-7500 lbs.

I have a 2003 HD 2500. 8.1 w/ Allison trans and 3.73.
Gets about 8 mpg pulling 29 foot Fountain w/ twin 502's. You know it's there taking off but after that you hardly know it's there. I'm a mechanic at a GMC dealer. Thought about the diesel but we had a rash of them in with injector problems about the time I was ready to buy so got the 8.1. No regrets. Have to drive that diesel allot of miles to realize any cost savings in fuel vs cost of engine.

My 2 cents worth.