3.08's, or 3.42's?

[Elpresidente]

I've been thinking of changing my stock 3.08 gears out for 3.42's. My truck is a C10 with a 700R4, I do mostly driving around town and I feel like the OD and high gears are bogging my truck down, as it shifts into OD at 35MPH cruise in town.
Will swapping gears give me more power, responsiveness and MPG? Or alternatively I could always drive around town in 3rd, lol.

[84burb]

OD (Overdrive) is primarily for open road or freeway driving. If you are just driving in stop and go or city traffic, leave it in Drive (third). You won't hurt anything because that's the way it was design to be used.

[79gmc15]

I've herd that 3:73 is perfect for OD combos.

[zieg85]

If your engine is a 350 and is efficient, meaning you get decent mpg than a 3.42 would be good.  OD ratio is .73 which would put final drive around 2.52 or so.  If you have a so so 305 that lacks power I would go to a 3.73 or 4.11 depending on in town versus highway.  IMO the 3.08 should never shift into OD at 35 and if it does there is something up with it.  I had a 3.08 in my 92 5.7L TBI and would run 1600 rpm at 55 and it would commonly downshift at the slightest incline,  I would routinely keep it in drive until I was ready to do 65-70 and actually got better mpg than lugging the engine in OD.  My $.02

[Elpresidente]

If your engine is a 350 and is efficient, meaning you get decent mpg than a 3.42 would be good.  OD ratio is .73 which would put final drive around 2.52 or so.  If you have a so so 305 that lacks power I would go to a 3.73 or 4.11 depending on in town versus highway.  IMO the 3.08 should never shift into OD at 35 and if it does there is something up with it.  I had a 3.08 in my 92 5.7L TBI and would run 1600 rpm at 55 and it would commonly downshift at the slightest incline,  I would routinely keep it in drive until I was ready to do 65-70 and actually got better mpg than lugging the engine in OD.  My $.02

It's a 350, and the MPG is actually not great but the engine runs like a top. I'll give this a shot, if nothing helps then maybe i'll swap out to 3.42's in the spring. Thanks!

[bd]

Is it shifting into OD or are you feeling engagement of the TCC?  Take a test drive.  When you feel it "shift into OD" at ~35 MPH, slightly depress the brake pedal - just enough to illuminate the brake lights w/o applying the brakes.  If it "downshifts," you're feeling the TCC engage and disengage.

Before incurring the expense to regear, you might consider recalibrating the governor to shift at slightly higher road speed. 

[square81]

I'm running an OD and changed my rear end to 3.73's, what a change. Upped the performance and milage a bit, works great around town and cruises at 2000 rpm on the highway at 65mph.

[Elpresidente]

Is it shifting into OD or are you feeling engagement of the TCC?  Take a test drive.  When you feel it "shift into OD" at ~35 MPH, slightly depress the brake pedal - just enough to illuminate the brake lights w/o applying the brakes.  If it "downshifts," you're feeling the TCC engage and disengage.

Before incurring the expense to regear, you might consider recalibrating the governor to shift at slightly higher road speed. 

Yes, that would also be something to look at. How would I go about doing that?

[bd]

The governor resides under a stamped steel cover retained by a spring clip just above the left rear corner of the pan (Fig 1).  After removing the clip, the cover will tap/pry off with minimal distortion if you're patient and careful.  The cover seals effectively with an o-ring and a little #2 Permatex.  The governor itself is a rotating hydraulic valve that's calibrated using weights and springs (Fig 2).  Pick up a governor recalibration kit and follow the included instructions. 

Kits are marketed by several vendors.  Here are two - http://www.summitracing.com/search/Department/Drivetrain/Section/Transmissions/Part-Type/Automatic-Transmission-Governor-Recalibration-Kits/Transmission-Type/700R4/

Chances are good that you'll only need to replace a couple of springs to recalibrate the governor successfully.  Depending on wear, you may also need to replace the plastic driven gear (Fig 3). 

[Elpresidente]

Ah, that's what that thing does. i'll look into it, thanks for the info.