Heavy Towing questions

[Jesse82nc]

So I have a 99 K1500 Suburban with the 5.7, 4L60E, and 3.73 gears (no G80). I've put some 32x11.5R15 tires on it, cranked up the torsion bars just a touch to clear the tires (the still rub on occasion on the front valance) and added an add-a-leaf to the back. Also replaced all 4 shocks and completely rebuilt the rear brakes and have new, good front brakes.

https://goo.gl/photos/NQ1KdFNNX3cJ5ZJo8

I have a 10k lb car hauler open-deck trailer I use from time to time for various purposes. It weighs in at just a hair over 3000 lbs empty, double axle, both have electric brakes (and I have a good brake controllers). I have put 1000 lbs on it several times and towed it hundreds of miles. And I put a car on it a few times that weighs about 3700 lbs. It always tows just fine, barely feels like the trailer is back there. I have mostly been on pretty flat ground with it so far though.

I'm just finishing up a build on my C6 Vette right now, and once that is done I will turn some attention to the truck. Over the next 6-12 months I plan to beef up the truck a bit and give it some more grunt. I plan to buy a nice bumper pull RV next year and we would like to take some longer trips with it, maybe over the mountains. This is the list of what I will be doing, any input on things that may help for towing would be appreciated. This list is by no means complete and yes I have more than done my homework on this and have sources for the supporting parts.
L92 6.2L engine with tuning and aftermarket cam (I tune with HPTuners) - engine is similar to the LS3
Rebuild 4L60E for towing / severe use and add large transmission cooler
14 bolt 9.5" SF rear end with 4.10 gears and electronic locker (change front to 4.10 as well)

 

[slowburb]

I'd want more gear with those tires and the towing you're talking about.

 

[90halfton]

I'd want more gear with those tires and the towing you're talking about.

Ya, more gear or less tire

 

[shovelbill]

I concur with the 2 gents above, especially "through the mountains". how big of an RV?......I hope those are load range E tires as well......basically you'll have a light duty 3/4 ton without the chassis. make sure your tongue weight is correct, i'd go with a load equalizing setup myself.............better safe than sorry.

 

[Jesse82nc]

I thought about going with 4.56 gears instead, but I do drive the vehicle quite a bit without towing as well and don't want to completely kill my gas mileage. I was thinking that with the extra power from the new engine (should be around 420 rwhp, 440 rwtq), I would be fine with 4.10 but open to considering it.

The mountains in question would be the Appalachians near the NC/TN area mostly (typically staying under 4000' and sticking to interstates). I don't think we would ever do a cross country and tackle the Rockies.

Most of the RV's we have been looking at would be around 7500-8000 lbs loaded with a hitch weight of between 650-800 lbs.

I was going to get some new wheels and tires soon, and was looking at the BFG KO2 tires in 275/70R16 which are load range 119 or 2998 lbs per tire, or in LT275/65R17 which are load range 121 or 3197 lbs per tire. Both are roughly 31.2" tall by 10.8" wide. My current tires make too much noise.

 

[Supercharged111]

Stock tires are 31" tall and I doubt your 32s are actually 32" tall. 4.10 would do you good. If you're going through the asspain of a genIV swap, may as well get do a 6L90 swap as well. HPTUNERS would likely allow you to piecemeal that together. I would not trust a 4L60 to handle that much power and tie it to that much weight. Have you priced the swap? I saw motor/trans/computer/harness packages in the 5k range. How much do you really like that truck?

 

[Jesse82nc]

I'll be spending about $10k when all said and done probably. A 4L60E with the right rebuild can easily handle over 800 lb ft of torque and can be specifically built for towing. A 6L90 would require a lot more changes, including custom shafts and custom shift linkages.

 

[Supercharged111]

800 ft/lb? LOL.

 

[Jesse82nc]

800 ft/lb? LOL.

I know of at least 2 guys running this setup with over 1000 lb ft of torque going through it - http://www.rpmtransmissions.com/page30.html

Both in C5 Vettes, it's the exact same transmission as the GMT400 minus the servo and bell housing. Most truck guys seem to forget that in drag racing, a lot of high HP guys use 4L60E transmissions.

 

[Supercharged111]

And there arw 1000 more cases of guys who can't keep a built 4L60 alive. You're ignoring how much of a load weight and prolonged abuse puts on a drivetrain. It'd be cheaper to run a stock 6L90 and you'd have much shorter shifts and a wider ratio spread. Think about it: that 6.2 will only run off of its own computer. The kind that is capable of talking to a 6L90 without modification. Plus the 6L90 holds the power in stock form with stock reliability. Sounds like a no brained to me.