Avalanche 2500 - 373 vs 410 gear ratio question
 

I have a 2003 Avalanche 2500 (4x4) w 373 axle gears and recently traded a 27 for 35 Fountain on a Myco trailer, towing weight (trailer & loaded boat) just under 12,000 lbs. The truck tows & stops very well but I've read that my truck is only rated to tow 9,900 lbs where the Avalanche 2500 w 410 gear is rated to tow 11,900 lbs. My question is, besides the 410 gearing, is there any difference between the 373 / 410 geared Avalanche 2500? More importantly, is there any difference in braking ability?

everything on the 2500 is heavier..bigger diffs,bigger rotors. 4 piston calipers and the rear backing plates still rot out like all the gm trucks lol..i really dont think the frame is any heavier tho like the older 80 gm trucks..i just had to repair the frame of a 2000 silverado that held the upper mount to the frame..(plow truck)

I had a 2500 Avalanche with 4.10s. AFAIK, there is no other difference besides the gear ratios.

Your current setup will be adequate for the new boat, but it's definitely not the same as a full truck frame vehicle.
I used to tow 12,000 lbs. with my 2500 Avalanche. I had slightly bigger tires which probably put me down to about "3.9" axle ratio. If you are running anything bigger than factory tires (245 pizza cutters) you will definitely lack some hill and passing acceleration with those 3.73s.

I strongly recommend EoH brakes for the trailer and make sure you pitch that POS factory hitch for a true Class-V hitch. You will also notice huge towing stability improvement going to 8 or 9" wide wheels if you have not already, AND add 2" spacers to the rear axle to match the front wheel track. I've posted most of that info in previous threads on the 2500 Avalanche that you can find with a search.

This is who you want to buy adapters from:
http://www.wheeladapter.com/dually_spacers.php

I have a 2500 Avey with the 4.10 gears and 33" tires. You should have no problem with the 3.73 gears, In fact I wish I had the 3.73's. Highway mileage is a moot point with 4.10's cause the engine just cranks rpm. My best mileage is at only 60 mph. Above 65 mph it drops to 11 pulling my 27' checkmate. If you want to feel like you put them in, just put a programmer on that engine. They are ridiculously de-tuned from the pickup/allison package and the 4L85E trans is very stout. There is 50-60 RWHP to be gained on that truck with a decent tune and cutting the torque management back. It will feel like you actually have a big block again.

Thanks for the responses. My biggest concern is safety but I don't want to replace the truck unnecessarily. Both my truck & trailer are inspected annually (beginning of boating season) as per provincial regulations so brakes and other safety issues are addressed. I plan to use my Avalanche as long as the only difference is the rear axle gearing. I can always replace the tranny, but it's never gotten hot, even when I got stuck in stop & go traffic when I first brought the boat home. That said, do EoH brakes make a big difference over surge (which I currently have)?

You probably have regular surge brakes on your trailer. EOH I hear is the best thing since sliced bread. I hate surge brakes on trailers. The surge system on my 2000 Eagle trailer is completely shot but I will be replacing with just electric. I know many people who have converted to this and they work just fine. Just make sure to unplug before dunking trailer.

EoH brake upgrade is worth every single penny. NIGHT and DAY difference.

That being said, I have two trucks with two different brake controllers.

MaxBrake on one.
Tekonsha Prodigy P3 on the other.

It sucks that MaxBrake is now out of business, as my MaxBrake controller it stops much better than the Tenkosha.

Keep in mind too that the stock OEM brakes for that year were phenomenal compared to anything you'll replace them with. I know it's an older truck but the original brakes last over 100k miles. So if you have the originals on there now you'll see a decrease in stopping power when you have a brake job done.

Greg your set up with the 373 is rated for 10,500 I think. I had a 2500 with 410's and it pulled my Chris Cat fine. The brakes are the weak link on the GMT 800's and they were same on the 2500 HD's. I changed my hitch and added air bags which helped alot...