Hope someone has heard of this problem before. Just bought a new 3750 LB trailer, and my truck won't pull it any faster than 100 KM/60 MPH. It tows nicely up to that speed, then the engine revs from about 2800 RPM up to 4500 RPM, with no increase in speed. And not a lot of pressure on the gas pedal. I have a 4.7 L engine with factory tow package. The truck will roll with the trailer hooked up without giving it any gas, and there are no problems with the trailer brakes or bearings. Any ideas?

 

Welcome to DF.

Let me put this in the 3rd gen Ram section for you, get you some help.

 

Sounds like its downshifting to compensate for a hill or wind. What gear ratio do you have, the 3.55 or 3.93 rear end? 20 inch or 17 inch wheels? How tall a tire? I have an 04 4.7L tow pack 4x4 quad cab. 3.92 gears, 20inch wheel with 33inch tire. I tow a travel trailer, weighs about 4400lb and also haul a 700lb atv in the box of the truck. In tow/hual mode, she'll hold 100km/h on the flat ok. Against a wind, or any grade uphill and she kicks down fairly soon... maybe 3000-3500 rpm. If I lose too much speed, and press the pedal more she'll rev right out. There isn't much more there though. The 4.7 is strong, but with a trailer or load she won't go fast or hold speed on hills or wind. Mine runs best around 85km/hr. That being said, if I rev her I can take it up to 120 on the flat... but its hard on it and the gas budget. This is only a 235horse engine moving a 6400 or so lb truck + trailer. I find a good long hill even without the trailer slows me down. The hemi would be the best towing choice, but the 4.7 will still get you around. They like to rev to make any sort of power... I also have a superchips programmer. Might help a touch, but I know I am starting at a disadvantage for the use I make of the truck.

 

Thanks for the info, I don't feel as bad now. I changed a really dirty air filter and took the trailer on a short 5 mile run on the highway, seemed a lot better, up to 110 KM at about 3000 revs, no over-revving. Will be on the highway for a couple of hours this weekend, so that will be the test. Thanks again.

 

Sounds like it could be all maintenance related? The thing's got to breath, especially under load.
Might be tune up time? When was the last time the Throttle Body was cleaned and the EGR replaced???

 

Tune-up time is right!

 

Just bought the truck from a dealer 2 months ago, of course they didn't do a tune up on it. Thanks for the info, will have my mechanic do a tune up next week.

 

Make sure that tune-up includes removing the throttle body and cleaning it, the EGR dumps crud right behind it which totally gunks the back of the TB.

I've seen mechanics not have a clue that the TB could get so bad on these engines and totally not even think about cleaning it...

 

You may consider flushing the rad and coolant, along with other fluids (tranny/transfer case/diffs). Also the spark plugs if its got some km on it.
You'll probably notice the temp gauge move when you hit any head winds or hills, especially at low speeds. Here on the coast, I see the gauge move from typical (just under the half mark with no load) to just over the half mark (maybe a 1/4 of the total gauge) when I climb the hilly mountain passes. This appears typical as these engine really work at hills. Just monitor it, you should be fine. I did a July 1st tow from Vancouver to Calgary and back with no issue on mine with the trailer. Slow on the uphill grades, but good otherwise. Once you get a feel for it and what your truck's normal is, all should be good. Be sure your trailer tires are at max pressure for the tire (measured cold), and away you go. If you run the P rated tires on the truck, then with the trailer you may want those closer to max pressure as well. (better weight handling, easier to roll so less fuel power requirements)

 

Met a family on the weekend in the next campsite, he had exactly the same truck, exactly the same problem. He said it's how the truck's computer is set up that is the problem, and that you can buy a different chip which allows it to change gears differently, so that you can tow at higher speeds. He also has a Durango with a Hemi, which pulls his rig easily, but is a pig on gas, so he rarely uses it.
Any further comments appreciated, thanks in advance.