using OD 4th spd. AT in tow rig: advice?

[larrybuck]

I have an '85 Suburban 6.2 D w intro...ed trans. We all mostly know with a car anyway the token advice not to use the OD at lower spds w hills. Of course as ecomodders, a lot of us are pushing the envelope for higher mpg. I am always short shifting my CRX, and rare is the time when I'm not in 5th by 30mph. I also try to skip 4th gear in certain down hill starts.

I am currently unemployed: I use the Sub. less than 1% of the time. With a 40 gallon tank, I have never filled it, and ONCE I did a 1/2 tank guess (mpg) trip w very good cheerful #'s ( I believe 27-30+ mpg poss. w some airdam, side skirt(under) work) Not bad for a fact. K model...thankfully a past owner put on manual hubs.


I have towed cars a couple of times, and it has done very well, in its only 125hp way.

The meat of what I'm trying to discuss here, is more Interstate (mostly 6% or less grade hills, etc...) Obviously, in urban/suburban ( no pun intended) areas; towing is stuck in the old classic 3rd gear ( that SLIPS in all AT's) I try to min. that mpg. wasteland as much as poss. In my freeway towing so far, I've towed a 2,600# vw Quantum wagon (want to make D powered!) on a typical tow dolly pretty well at 45-50mph in 4th on the freeway. With my low HP; obviously, I'd change down to 3rd myself, if it were clear I was going to be 30-35mph..ish going up the next hill.

The Sub. not towing wants to upshift itself into 4th at about 37mph. With what I have towed # wise; I figure I could do a cross country type trip being in 4th 97 % of the time attempting a general 50 mph average cruise speed.

NOW; we change the picture: This is a K10 Suburban, not a K20! What if I now add a 26ft. enclosed Wells Fargo enclosed trailer w that 2,600# car inside? Less aero, and more weight. Could I still hope (dream?) to achieve the above paragraphs mojo staying in 4th maybe 89-92% of the time? I've not ever pulled that much weight with an AT before... always w a stick! That was w a '69 Ford F250 w 360 V8 averaging 11.5 mpg towing cross country at 40mph flat land towing cruise.

What mpg. should I expect? Is the GM setup strong enough? I've read that Suburban's like mine can be rated to pull a total of near 13,000#'s! Most of all the near vintage to mine, are all AT's. Could a stick trans. from a D PU swap onto the 6.2 easily, and would that be better?

I don't care that my setup is kind of a slug. I like that by itself, near 30mpg highway is there... what do you think I'd get w the bigger tow I've described? If I needed more speed, and more $$$$; I'd probably lean toward a late 80's, early 90's Dodge w Cummings 12V as I hear 22mpg is possible at 70mph towing a 30some foot 5th wheel travel trailer!! How well does a later model Duramax do???

So many questions, and life is so short! I thank you for your responses in advance... and thank one of you who was nice enough in a NICE way to teach me how to PARAGRAPHS here, as I'm still fairly new to computers!!!

[JasonG]

Not sure which tranny you have. If its a TH700 do not tow in OD. I blew one up towing a 21 foot trailer that way.
In newer trucks the MTs are rare. I have only seen one other than mine. The new Duramax with the allison is bulletproof but not cheap.

The K10 is basically a half ton PU with a different body. The K20 is a 3/4 ton. You can look up the towing capacity on most hitch sites once you know which tranny and rear gears you have.

For a WAG I would say 8,000lbs will be your limit.

[me and my metro]

I built a 84 K-30 with a Suburban frame, one ton axles, n/a 6.5 Diesel, and a properly built 700r4. I tow in 4th gear all the time, I have 4.56 gears and 33" tires. The truck gets 17 empty and about 11 towing my 35' Avion pull trailer( 10,000 lbs). The point is you can tow in overdrive with a correctly modified 700r4 as long as it doesn't hunt between 3rd and 4th.