As the title says, I have 2003 QC 1500 4x4, with a 5.7.

Years ago I levelled it, and have run 35's ever since. Still goes along just fine unloaded, mileage is/has always been crap, but that's expected.

Just picked up a new-to-me travel trailer that is a bit heavier than the last two I've towed with it, not heavy by any means, but is creeping into the 7000# range. I bought the truck 8 years ago or so, and she's been a champ. Sitting at 215k on the clock now.

Here's the scenario: I usually always towed around 65 mph O/D off (mostly to minimize shifts), and that kept me in what I thought was a good RPM for torque and H.P., right around 25-2700.

Now, I'm in a pickle. To get me in the same "powerband" with the newly added weight, I need to keep it up closer to 70 on the speedo, and with uncorrected MPH's means I'm going 73-74.

Mileage is almost comparable towing at that speed, but I'm just wondering if a steeper ratio would let me leave the O/D on, and not have to work the engine and tranny so much.

I rebuilt the stock rearend around 18 months ago, so I guess I know my way around it.

Just looking for pros and cons between 4:11s and 4:56's for my application, I suppose. '

Or maybe I'm looking for a good excuse to go find a different truck... 8 years seems like an eternity


Thanks guys! Sorry for the very long post

 

Been there. Done that. Lol. But I was still on stock 20 inch wheels and tires Im now in a diesel for towing (but kept my ol girl.)
For me it wasnt worth it. RPM were to high. 3400 to 4000 between 60 and 70 mph. Tank of gas every 200 miles. With overdrive on. I was towing about 7g as well.

 

if i understand this correctly...you want to raise the rear end ratio to be in the ideal rpm range for 65mph...

how many rpm do you need to raise

 

Just another note...When i was towing with the 3.73 and i came to a stop after freeway run, I had the odour of gear oil at the back of my truck....no leaks...i guessed I was boiling the gear oil ànd the odour was coming from the vent tube. Thus I decided on 4.56. Used this setup for 3 summer seasons until i found me a very nice 2012 CTD. Would never go back to a gasser for heavy towing now. Good luck !

 

Well, at 70, I'm around 2100 with O/D on, way too low, and the truck wants to constantly shift in and out of O/D on flat ground.

 

The rebuild of my rearend was due to me backing into a lake a little too far to load a SeaDoo in the bed. Got stuck in there long enough to fill the housing with some water. I never realized the fill hole is just a dumb grommet.

I had the same boiling action happen the next time I towed my trailer very far. It just happened to be on a 90* day. Got to our destination and there was an oily mist all over my equalizer hitch and front of the trailer. Bad news was, I waited too long to fix it, and burned up a bearing.

I figured I could swap ring and pinions in both the front and rear diffs for about $700 in parts, and my labor... which is less than a couple payments on a newer truck.

 

Both ends need to be changed (or never use 4WD again). 7,000# is about at the limit for 35s and 4WD. 4.56s will get the mass moving, but will suck gas even worse at highway speed.

 

imo its not made to tow that much in od...use tow haul, slow down ( your towing 1000lbs more than the truck weight) and the rev's will be golden...save $3000 in changing out the differentials.

 

I stated above that I tow with O/D off.

So if I understand you the trailer shouldn't outweigh the truck?

 

Most trucks tow ratings are more than the truck weighs in any event. Also, it isn't so much getting all that mass moving, as it is being able to stop it in a controlled manner. A 7k+ trailer is likely rapidly approaching your maximum safe weight. Ever consider stepping up to a 3/4 ton truck?