Personally, I think it would be fine to leave the 3.08 gears in.
With a 4x4, if you want to change to 3.55 that means changing both front and rear axle ratios, so think in terms of the parts and labor for all that.
And you are doing this on a vehicle over 20 years old with how many hundred thousand miles on it? There probably aren't enough operating miles left on it to pay back the "benefit" of changing the ratio.
If you actually care about performance and gas mileage, you probably will not choose to put on the 35"s. The bigger tires will hurt gas mileage regardless of what you do to the ratio, and will also hurt performance. The lower gears would help offset the performance penalty of the larger wheels.
Bigger wheels will give you something that "looks cool" and might perform slightly better in some off-road conditions, but will probably be mostly inferior to the stock tire size for normal street use.
What gets really good mileage is skinny bicycle wheels, or the skinniest wheels and tires that will manage the load rating for your vehicle, which is probably what the OEM tires are. Tire rack lists P215/85-16 or P235/85-16 as OEM tires. Those really are a good compromise for gas mileage and performance if you care about it.
--- I checked out the 4lo.com site the previous poster recommended, and for P235/85R16 the height is 31.7", so replacing that with a 35" gives the "effective ratio 2.79" and to maintain the same effective ratio you'd need to swap to around 3.4:1, or if you want lower gears about 3.7:1 is good for better crawling performance, and keeping the 3:08 is ok if preserving highway mileage is more important.
