In OD or not?

[FULLSIZEChevydotcom]

I was just wondering if I should be driving in [OD] Overdrive or not in regular city traffic simce I

                                              have a suspension lift and running 35's now. It still has the stock gearing. Should I be in

                                              regular [D] Drive? Someone mentioned that to me recently, I was asked why I drove in OD, I've

                                              always driven in OD since I got my truck, is this hurting the transmission?

[Frank S]

One thing I noticed with my '93 1500 before I got the Zr2 is that it would kick out of overdrive very easily in speeds under 45 mph.

I don't know if your transmission does the same as mine but I always drove in 3rd until I hit speeds of over 45 and then would put it in D.

[vhato]

I am not sure how true this is and it may end up starting a whole mess of opinions, but at least we will have an answer.  According to HyperTech and West Coast Differentials, when LARGE tires are installed and gearing has not changed an engine runs lower in the rev range (Obviously).  On a carburated engine with a 3 speed auto this is no big deal.  It just bogs the engine down.  A fuel Injected Engine is different I am told by HyperTech.  Reguardless of programming whether stock or modfified.  They said that in O.D. the computer is told to back off the timing (retard spark, use less fuel, etc) at certain but different speeds for fuel economy.   With the extremely high gearing (do to large  tire swap and stock gears)  the engine runs below its intended RPM Range at 55 and 65 MPH, thus forcing you to use more throttle to maintain speed while fighting the computer.

 Another POSSIBLE problem is my brother-in-law has owned a transmission rebuild company for 13 years.  He states that with the stock gears and large tires 33"+ extra wear is placed on the transmission to transmit engine power to the rear wheels.  Due to extra throttle from the driver because it is slower.  This in turn causes heat to build up in the torque converter,  which is locked in 3rd gear sometimes and in O.D. all the time which flushed most of the fluid out of it and into the tranny.  The Hot fluid is thinner (even with a cooler) and causes the parts not to be lubricated as well  which wears out the "Band" and "Clutches" and breaks the "Planatary Gear" on 700r4 and 4L-60E Transmissions.  

  Of course neither of these things really apply to whether it is better to ride around in O.D. or in 3rd.  I dunno, this is just some education I was given when I lifted my truck and a few years of my brother-in-law fixing 3 4L-60E Trannys.  I learned this time.