Just bought a used 4x4 Tahoe 2006 loaded Z-71 with all the heavy duty towing packages. Has a towing capacity of 6800 lbs w/ the 5.3 engine. Prior to purchasing from dealer, I was given incorrect info and was told thaat the vehicle had 373 gearing. Turns out it has 342 gearing. I live in Colorado and have a cabin at 10000 ft. I tow a 3500 lb boat/trailer appx 5 miles to the lake in summer and tow a loaded 4- place snowmobile trailer (appx 4000 lbs) about the same distance in the winter. I usually tow the boat to Lake Powell once a year. Research has told me that the only options that year were either 4.10 or 342 gearing. I have not tried towing anything yet and have not even had the vehicle in the mountains yet. Am I going to hate this vehicle when towing anything? How much would it cost to have the gearing changed?
Why change it???
Seems like the vehicle you have has MORE then enough power to tow…even with the current gear ratio. I tow a trailer several times a year and FAR GREATER DISTANCES with my Toyota 4-runner. Weight of my trailer is about 3200lbs. I don’t think you’ll have a problem at all. Leave it alone.
You’re only towing for 5 miles; use a lower gear for the steep slopes, if you have to. I would not bother with a different rear end.
Gee, only a 5.3 litre V8 huh? You’ll never be able to tow anthing with that, I’d swap in a V-16 from a military tank 
Kidding aside, yes you’ll be fine with ONLY 3.42 gears. In fact the difference between 3.42 and 3.73’s is minor if at all noticeable. The 4.10 gear will be thorn in your wallet everytime you go crusing on the highway, because you’re going to lose a few mpg.
Changing gears can be a problem in itself because they will whine if not correctly installed, and you can expect to spend at least $500 to have it done. On top of this, you need to correct for speedometer error because of the change of gear. Let them be.
Double that, since the front differential would also have to be changed.
The trailers are well below the stated towing capacity of the vehicle, assuming the figure accounts for the axle ratio. Add a large auxiliary transmission cooler for additional protection.
If it came factory equipped with the tow package it already has an oversized tranny cooler installed.
Your 3.42 rearend ratio gives you the best mileage when NOT towing.
That said, you should be using the ‘tow haul’ mode when towing to keep the tranny from ‘hunting’ and overheating.
When towing (especially on steep grades), the engine will downshift more often and thus burn more fuel than one with a 3.73 RE.
The 3.73s and 4.10s are better suited for pulling heavier loads as there is higher torque which puts less strain on the tranny.
However, as was mentioned, the truck will burn more fuel with a 3.73 and a 4.10.
Do not expect good fuel mileage with a truck whether towing or not. If you’ve had a truck before you will already know this.
How did you find out it has a 3.42 instead of a 3.73?
What is the RPO code on the sheet in the glove box?
3.42-GU6
3.73-GT4
4.10-GT8
I’ve talked to quite a few RVers over the years who have towed with the Tahoe and Yukon and just about all said the 3.73 was most favorable for towing travel trailers, and 4.10 for duallies (with diesels) with 5th wheel trailers.
As NYBo said, your looking at $1000+ to change the gears in front as well as rear and like Dave mentioned, if the gears are not professionally installed the rear end will whine and it is extremely hard to fine tune.
Now, you likely won’t be towing those types of trailers and the weights you tow won’t have a real affect on performance other than what I mentioned.
Keep in mind you have to adhere to your state towing laws/requirements too. Trailers over a certain capacity are required to have their own brakes. If electric brakes, I would recommend installing a quality brake controller in the Tahoe.
I imagine the boat trailer is equipped with surge brakes so you wouldn’t have any use for a controller for it.
I use the popular Prodigy brake controller in my Tahoe with my 21’ travel trailer and it works beautifully. Very easy to install. (just plugs into a electrical connector in a small covered box next to the left foot rest below the brake pedal)
I see what you mean about having a 3.42 or the optioal 4.10.
I guess GM figures the extra 10 hp will compensate for not having a 3.73.
Bottom line is you should be ok with what you tow there.
Sorry group, got a little carried away.