You're going to see some more fuel being used up but it's not going to be all due to the gear ratio.  Matching the gear ratio to your tires will help improve your MPG usage, but remember you're going to be close to double the weight of each tire/wheel compared to the stock tire/wheel currently on it.  Because you're going to be moving more weight (more rotational mass) you're going to lose any MPG increase due to needing to move more weight.

But like you said, it's a weekend toy.  You're not going to notice any immediate increase in fuel consumption if you gear it right.



Kris  

Do you think going with the 19.5's would be a better way to go? and using 4.10's,I Think the diameter is about 33"
Plus I would think the tire /wheel combo would weigh less.With the added weight of the wheels/tires, are those big brakes adequate to stop this already heavy truck?
Thanks for the info, better to spend wisely in the current state of the economy.  

19.5 Alcoas or alloys compared to stock steel wheels shouldn't be a huge difference in weight, maybe even lighter. But between 16s and 19.5s, if they're both alloy, the bigger ones are going to be heavier.

The consensus on here seems to be that the best newer-model Cummins is the '04.5 or '05 model.  

It seems that the best truck to buy would be a 04.5 or newer 5.9l and use the 19.5 wheels for the Big Rig look.
American Force makes some nice wheels the bolt on so you don't need 10 lug adaptors,and probaly stick with the 4.10 gears, in your opinion, is this probably the best way to go?
Thanks  

Rolling on 19.5's with an overall tire height that doesn't excede more than 33 inches should be fine with 4.10's.  Over 33 inches and you need to swap out your rears or suffer slowness off the line and it eventually damage to your tranny/TC.

You might also want to make sure you don't have any suspension parts being rubbed by the new shoes (tires) when you turn your steering wheel from stop to stop.



Kris