I purchased an 81 Chev 1-ton crew-cab (4-dr 6 pass) 8' long-bed dual rear wheel GAS in 1989 and put about 110,000 miles on it before I bought my 03 Dodge QC LB SRW in July 03. Some of the positives and negatives of DRW vs. SRW:
Postives:
1. Very stable on the road while underway, empty or towing. Better in windy conditions than a SRW.
2. 2 extra "spare tires" if you're very far from nowhere and have the time and ability to take one of the outside rear tires off and mount it somewhere else.
3. A 1-ton crew-cab long-bed DRW is a PREMIER long-haul over-the road vehicle on long highway trips, especially in wide open spaces. Set the cruise control, put your feet up on the dashboard (in a manner of speaking) and float along.
4. I once foolishly drove into a dry sandy riverbed in my 2WD DRW, and of course got stuck. I managed to round up about 10 small children under the age of 12, and clustered them all in the rear of the bed. Voila! It drove out as if it were a 4WD! I don't think a SRW would have done it so easily.
5. With a DRW, you will become an EXPERT at BACKING into parking spaces. It's much easier.
6. Vehicles following behind you at high speed on freeways and the Interstate tend to stay farther behind and leave more stopping distance between you and them, than if you're driving a passenger car or a SRW pickup. We've surmised that it's because they can't see around you when they're too close, so they stay back about 1/2 of the distance they OUGHT to stay back, rather than the 1/4 of the distance they otherwise stay back if you're an SRW.
7. The DRW vehicles have more rear red and side clearance lamps than the SRWs, which I consider a plus.
Negatives:
1. Don't get too worked up about "increased carrying capacity" of the DRW; that is mostly a myth. Most of the owner's manuals say that the carrying capacity of the DRW is the same as the SRW, MINUS the weight of the extra two wheels and tires, extra shackles, springs, etc. In many cases the carrying and towing capacity of the DRW is LESS than the SRW. Don't take my word for it; look at the manual.
2. Fuel mileage is MUCH poorer with the DRW than with the SRW. There is too much increased rolling resistance with the DRW. I experienced about a 30% decrease DRW vs. SRW with the gas truck; expect about a 20% decrease with the diesel.
3. I once ran out of gas at a stoplight on a level city street. I tried to hand-push the truck over to the curb. Couldn't do it. Couldn't get it started rolling -- too much resistance on the pavement.
4. A DRW is about 18" wider in total -- about 9" on each side. I took off the left rear fender (fiberglass) on a post in a outdoor parking lot after I'd been driving the vehicle for 6 years!
5. If you rotate tires to maximize tire mileage, then you have to buy 6 new tires at once, rather than 4 (or 7, if you include the spare in the rotation).
6. I had a VERY difficult time getting ALL FOUR rear wheels balanced together for a smooth ride. I probably spent about $800 to $1,000 over 13 years trying to get a smooth ride on level pavement with an unloaded truck. The problem was not that there was a constant shake or vibration, but rather that VERY SMALL inconsistences in weight, "roundess" or "trueness" of the rear wheels (the steel rims), and in the small variances in the balancing procedure itself would cause the rear wheels to vibrate in a rhythm -- say for about 5 to 7 seconds once every 30 seconds at 60 mph -- rather than all the time. I finally gave up on ever getting all four to run "true" to each other, or to run "true" in pairs. Of course, if you DO happen to achieve "harmonic" balancing after much effort and expense," you can't rotate your tires. And my Chev used 16. 5 x 9. 0 tires, rather than 17s.
7. The inside rear wheel is difficult to check air pressure, or to fill with air. Even if you line the wheels up so the spaces in the wheels match, some garage doing a brake job or rotating the tires or other mechanical service will remount them so that they DON'T match up. Then, you can either live with the inconvenience, or remount them yourself. They're very heavy, very awkward, and garages use an air gun to "weld" the lug nuts in place. In order to check inside wheel air pressure, I finally made my own air gauge, at a cost of about $20. 00.
8. The DRW is VERY rough riding when empty. It has twice the surface area in contact with the ground, so the rear tires generally have to be run at a lower air pressure than the front tires, when running empty -- or, you get tossed up against the ceiling when you hit bumps. At least that was my experience with the Chev. We once had to drive 35 miles on a dirt washboard road with six passengers and luggage. We were limited to about 10 mph. Anything over that and the rear of the truck started to drift sideways across the road as the wheels would not stay on the ground. Of course, the '81 Chev does not have "progressive" rear leaf springs.
9. Some toll roads charge by the wheel, rather than by the axle. This usually isn't common in the U. S. However, in Mexico -- where we traveled about once-a-year for about 8 years -- tolls were based on axles, and on the number of wheels on the road. We paid less toll than a 3-axle truck, but considerably more than a four-wheel passenger car, notwithstanding that we were a passenger, rather than a commercial vehicle.
10. A 1-ton crew-cab long-bed DRW is an absolute pain-in-the-neck in cities and other congested areas. Parking garages are forbidden territory, as are downtown city streets. For street parking, even with the outer right-hand rear wheel touching the curb, the outer left-hand rear wheel and the left-side rear fender are dangerously close to traffic. Occassionally, I used to put the right-hand outer rear wheel up on the curb when parking. Of course it's illegal, but fortunately I never got a ticket (for that).
11. Drivers pulling into parking spaces next to you in outdoor parking lots tend "Not to See" the bulging rear fender.
Attention: TDR Forum Junkies 
I have found that in NY, MA, NH and ME that they charge you for an extra axle on the tolls. It is not a huge deal if you do not use them every day, but for a daily ride, it could get expensive. I have not regrets at about having a dually. It fits my needs and I would not change a thing if I had to order it again. After all these years, I finally got it right
