quick qestion

[alteredspeed]

I have a 1988 gmc 1 ton dually. Bought it 5 months ago with a jasper rebuilt 6.2. I orginally thought it was a 700r4 but quickly found out it was a th400. I just got done with the body and paint work and am taking it to tennesee on thursday towing a car hauler. On the highway the rpm seem a little high. Im assuming it has 4.10 and I am running 235\83\16 tires, which are relativley tall. Should I be conserned. Im also used to gas engines and not the 6.2. By the way it is an old body style 88. Is it worth trying to find a 700r4 when i get back? Thanks for the help.

[john8662]

If you pull a lot the TH400 will serve ok, but the highway revs are what will eat fuel economy.

I recommend a Tach.

A built TH700 would sure be the ticket.

J

[alteredspeed]

So it should be fine to run 70 down the highway. Just keep aneye on temps and oil pressure.

[DmaxMaverick]

The 6.2L is perfectly happy running against the governor all day long. The only thing that suffers is fuel economy......and your hearing.

Yes. As long as the gages stay in check, all is good.

[joescj5]

I don't know if GM ever put a 700r4 in a 1-ton. In my mind it is at best a medium duty transmission. I would be leary of running even a built 700 if I was doing much towing at all.

The 4L80 is the overdriven version of the TH400, and is a beefier transmission to start with. I am unsure if they are all electronically controlled or not. If they are all electronically controlled then you would need a stand alone tranny controller.

You could also step up to a new 4L85E, it is GM's version of a beefed up 4L80E. It is what they put behind their 8.1L gas engines, and could really be the ticket for a rig that sees heavy use.

My simple advice, is run the TH400 till it croaks. The 700R4 isn't beefy enough to warant a swap, and unless you run a LOT of miles the 4L80E or 4L85E would probably be cost prohibitive (It would be worth running the numbers through a mileage/cost calculator, I believe there is one somewhere on this site)