You should have no problem towing that. I tow a 20 foot pontoon (think parachute behind the truck) not so much heavy (approx 3900 lbs) but a lot of drag and it tows great. Also towed my brothers 26 foot rinker (approx 5600 lbs) and the surge brakes for the trailer were non existent. (he has NEVER put in brake fluid and has been dry for 2 years)
the .75 4th gear ratio makes it into a 2.94 gear ratio, when combined with my 3.92s. My old 83 W150 with 318 4 barrel, smaller tires, has a 4 speed granny low, 3.23s, weighs about 600 pounds less the the Dakota, and will tow most small hills in 4th, while the Dakota goes back & fourth between 4th and 3rd. I thought the purpose of tow haul is to keep it from excessive shifting, but no luck with this 4th gear ratio. DOH! Unsat! They need a real gear ratio for forth, don't now exactly how they'd accomplish it but if they had about a 3.30-3.40 gear ratio in fourth, that would get it up the small hills with a trailer, and most large ones without the trailer, and it wouldn't hurt to make the ones with 3.92s have a bit taller 5th, like a .65. Of course Dodge doesn't want to build them differant for each combo, it'd work better. I've thought about the Frontier 4x4 long bed 6 speed, too bad they can't make leaf springs right, the mirrors are small, and I don't like their little center console. It's either that or smaller tires, for the Dakota, keeping in mind of the load range, making sure the smaller ones will hold all the weight. Can't see putting 4.1s or 4.56s into this for the cost, even if my step bro does have a trans shop and might be able to cut me some slack
Just keep in mind a couple things: 1. The 545 seems to be a good tranny from a reliability standpoint (more important to me than anything else), and it does have excellent shift quality. 2. The truck will tow anything you want to within the stated factory specs (i think up to around 7000 lbs equipped correctly). It may not "tow it like its not even there...", but it'll do it. For someone that tows upwards of 6000-7000 very often, more truck might be better suited, but thats a personal call.
Read over at pickuptrucks.com, they did a 1500-series comparison recently. Hooked 6500 lb (i think) trailers up to each truck, on flat ground and couple different hills. On the steep hill climb, most, if not all, kept accelerating after shifting into 2nd. Not the Ram...that 1.67 second gear kept it at the same speed. They made a big deal out of the Ram only being able to hold speed in 2nd. It was a steep hill. Nevermind the fact that it did pull the trailer, that it would pull 99% of what we would need it to, it just would not pick up speed when all the others would (and even the gain wasn't that much). So you have to keep perspective when talking about these kinds of things.
Also, its important to keep in mind that I purchased my truck for about $22K (sticker $29500). Theres a reason Dodge could do this for me, and using the 545 instead of designing all new trannies every 5-7 (or whatever) years is one of the reasons. If Dodge had designed an all new 5 speed for this truck, it probably would have cost more. I don't know if they can modify the 545....I assume they can't do much with it because they would if they could. So for the price, its a pretty compelling combo (the 4.7 and 545).
