I personally wouldn't go over 6", just because of the increased tendency to want to roll when turning.

 

A gas engine 1/2 ton 4x4 is your best bet. The diesel and its Allison transmission adds an extra 900 lbs. to the weight of the truck which is not a good thing for offroad use as it puts more stress on the frame, steering members, suspension, wheels, and tires.

Diesel is great for towing a lot of weight up grades at 60mph. For offroad use a gas 4x4 is going to have a low speed range that makes it easy to have enough engine RPM's for power and still crawl over rocks at 3mph (or less with a manual trans).

The cost of fuel for gas versus diesel is going to be little different if you are not hauling heavy loads. My last check found diesel to be priced on average about 11% higher than gas and with diesel the mpg is going to be 20% higher so for most purposes the cost difference is going to be slight. For offroad it is much easier to find gas in some small out of the way town than it is to find diesel. Add in the $5k extra cost for a used truck with a diesel engine and you will never be ahead dollarwise with this approach.

For offroad use the lighter the truck and the lighter its axles and wheels and tires the better. The main advantage with racing wheels is their much lower weight which puts less stress on the suspension components.

Raising a vehicle may be important for bigger tires but bigger tires do not improve offroad performance and can often hurt it by making your gearing 10-20% higher and making the clutch or torque converter work a lot harder.
Raising a truck also is going to hurt gas mileage by at least 10% and probably more by increasing both the turbulence under the truck (which is why new 4x4 trucks have air dams, and raising the overall profile. It also takes more gas to keep the larger tires turning and most of the big tires guys add to their truck look bad but also have a high rolling resistance and a lot of squirm so the tread life is terrible (often 20K or less per set) as well.

Raising a 4x4 vehicle also raises the center of gravity and makes it much easier to roll, either going around a corner at speed, on wet roads or on ice, and offroad with trails that are seldom level. Whenever I have been offroad on some trail with a 10 degree side pitch I have been very grateful to have had a truck that was not raised and wishing if anything that I could lower it even more for that stretch.

In all my years of offroading all over California, Arizona, Nevada, and Utah, I have never been in a situation where it would have helped to have a raised truck and bigger tires. Many times I was glad I had not raised the truck as it would have greatly increased the odds that the vehicle would have rolled and I might not be typing this now.

I photographed a Hummer event in northern CA at an offroad park near Hollister. I saw drivers struggling through sections even with the front and rear locking differentials, raised vehicles, and monster tires. After the event was over and the park was opened to the general public I saw a family in a Suziki Brat charge around the same sections with zero difficulty. You could by 15 Brat's for the price of one of the Hummers not to mention the difference in fuel costs.

Raising a truck also usually puts a lot more stress on u-joints and the last thing I want to do is make it more likely my truck is going to breakdown in the back country and I will need to walk out and find a tow truck operator willing to go back and haul it out. I did this once when a front spring mount broke on a 4x4 truck and I was incredibly lucky to find a backhoe operator in the middle of nowhere that had a DC arc welder and who welded the mount back onto the frame while my wife and I had some of his wife's fresh cherry pie. I do not count on being that lucky as a rule.

There is a reason why most dealerships will not sell a used truck if it has been raised. They simply do not want the liability.

I know that many guys lift their trucks and have sold themselves as to why it is important and all the benefits but whenever I see a truck raised 6" or more I figure the guy never takes his truck offroad other than into some farmer's field.

 

I'm new to the forum and need to ask a question. I have a 2005 Silverado 1500HD with the 6.0L engine. For the last year, I have been getting a message "Service 4wd". When the message is displayed, the unit will not shift into 4wd. I read some posts and removed the switch on the dash and re-soldered the terminals. The message didn't appear for 30 minutes and before it was coming on after about a minute of driving. I cut the truck off and got back in about 15 minutes later and after about a minute the message has come back. What should I do next if you have any ideas. Thanks