I have a supercab short bed with a 4.2 V6 4X2 and 331 gears.I will be pulling a travel trailer that weights around 4500 lb. My question is do I need to go to 355 gears or 373. Now I run around 2100 rpm's at 55 mph with overdrive locked out.Can anyone tell me what rpm's I would be running with each of these gears.Thanks for any help you guys can give me.

 

You don't "need" lower gears, but it would not hurt any either....

I tow a #4500 travel trailer (that's fully loaded too...) with a 5.4 and 3.55 gears with 31" tall tires and do rather well... Yes, I'm still reduced to 2nd gear on the long grades, but I can maintain 50 mph very easily and I'm far from having to 'mat' the go pedal...

Even on the flats, the truck likes 3rd gear at around 60 mph (in my case that's running about 2300 rpms) It'll do that all day long and net me around 11 mpg...

It's not the weight that will get you however, it's the wind resistance of the trailer.... Hit a little head wind and you will probably find that the V6 and 3.31 gears will require you to press that go pedal a bit more! Might even downshift into second if it's strong enough...

If you did go up to the lower gears, figure on about a 200 rpm difference for each lower gear set. This is assuming a 1:1 trans ratio and the same size tires of course....

IMO, I think you will struggle some with the 3.31 gears (even assuming a 29" tall tire)... You'll get down the road, but it'll require some revs to maintain and that will mean second gear a lot of the time..... If you decide to swap gears, don't even think about the 3.55's... Move right up to the 3.73 and even consider 4.10's.... Trade off there is running about 2600 rpms in 1:1 at 55 mph.... But, I'll bet you won't downshift near as much out of third gear!

Mitch

 

Yeah, I'm really considering putting 4.10ish gears in to replace the 3.55's I have. I'm pulling a 5600# dry trailer though. Wife and I decided we'll be keeping this truck for a while so I want to make it better suited to tow with. I would think with that v6, 4.10's would be better since you're lacking a bit in the overall power dept. You'll get better pulling power off the start and probably be able to hold a higher gear on flat ground. Your overall gas milage might take a dive though. For me I'm thinking the towing gas milage wil increase while the regular milage will go down a bit. If I decide to do it (most likely) I'll post results here for everyone.

edit: 3.73's would probably be a good medium ground for you now that I think about it if you're concerned about the rpms running too high for your comfort in 3rd. I don't think you'll be over 3000rpms though with 4.10's. Probably closer to 2800. Ask over in the powertrain forum, I believe they could help you calculate the exact #'s.

 

If that 4500lbs is total weight not too bad, but if thats the dry weight and you add approx. 1000lbs with gear, people, water etc. and get around 5500lbs. That is too much for a 4.2 period in the motor area, nevermind the gears. I mean you can tow it, but comfortable range and not stressing your engine and drive tran. 5,000 max for that 4.2

What do you say mitch?

 

Thanks for all the information. My trailer has a dry weight of 3400#. I just ordered 373 gears. Will I have to go to the dealer to have the speedometer recalibrated? Again thanks for your help.

 

You could always just purchase a tuner to change the speedo yourself.

 

I agree with Colorado Osprey, if you would get a tuner+ the gears you can change the transmission shift points, speedometer, octane rating, exec. 3.73's are probably going to be a decent choice for you. It should give you decent towing power and overall MPG. Good luck and let us know how it turns out.



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