Friend your towing capacity is based on your vehicle and the best place to go for this kind of info is your users manual or the vin sticker inside the door of your truck. These values vary from truck to truck depending on options for instance a 2 door v6 5 spd manual will be able to tow more that lest say a v8 4x4 crew cab AT due to more of the power being delivered to the ground instead of getting stripped by extra vehicle weight more drive line components and such and that's all before you add things like people fuel gear food all of which need to be considered when hooking a trailer up to your truck. Now if you have modified and put some "go fast" goodies like a cold air intake open exhaust power programmer (engine tuner) transmission shift kit extra trans coolers(heat kills auto trans) airbag suspension then skies the limit you could potential-ally approach the limits of a certainly a 1500 or even close to a 2500. The biggest thing that to keep in mind when towing the heavier items is that sooner or later you have to stop so a electric trailer breaking system is a must.. our Dakota's just don't have ass to whoa down the big stuff even with break caliper and disk upgrades.
If it helps, I towed a 6x12 u-haul with 2500 lbs of woodworking tools 650 miles including the passes between Ca. and Or. and my 2008 Quad cab Laramie V8 4x4 did great. The bed had a few hundred lbs of misc. tools in it also. The Laramie that I have is rated to tow 6500 lbs.
Properly equipped the Dakota can tow up to 7000 lbs, but as Big Dog says you have to analyze your truck and your load carefully to figure out your own sitch. Altho I have always been told that an automatic will always tow better than a manual because of the stress on a clutch. Certainly the capacity of the Subaru automatic has a higher towing capacity than the manual.
I towed my 96 maxima on a car dolly from uhaul as well as on the double axle full trailer with the electronic brakes from uhaul. I must say the car dolly was nicer because the full trailer dropped my back end a lot more than I was liking, but in both instances, my little v6 pulled them just fine. When you tow anything you want to keep in mind that you have the extra weight so of course don't drive like you normally do and stay a little farther back for stopping. My truck was completely stock at the time, but now I have a cold air intake, dual rear exit flowmasters, and a stage 2 jet chip. only other thing I would recommend is stiffer rear suspension because the front end does wanna lift a little more. had that issue when I had 1400lbs of sod in the bed of my truck (keep in mind my truck is the crew cab, short bed).
Have towed 16 foot travel trailer with 2005 crew cab Dakota with 4.7 and pulling weight is about 4200 pounds wet. No problems unless temp outside is over 85 degrees then temp gauge goes up some about 3/4s . Did 4,000 mile trip, super steep hills caused temp to go up. Auto tranny shifts seem to want to rev high on steep hills when in reality lower rpm shift would work fine. Can tranny be tuned to work more efficiently?