I'll try this one last time.
I live in a town, like rbatson, that has frequent stoplights and a lot of traffic. If I leave the transmission in OD while driving in town, the tranny will shift into OD at every opportunity it gets...usually around 35 mph. At this speed, OD pulls the revs down low...like around 1500. My power band begins right around or just below 3000 rpm. When the car shifts into OD at this low of an rpm, it puts a heavy load on the motor and gives the sensation that the motor is bogging.
As it is, in this type of traffic, I usually don't have opportunity to cruise at 35+ mph for very long as someone is always slowing down traffic. As soon as I drop my speed, the car shifts back into third gear. Then, when I get a clear lane and step on the accelerator lightly to pick up some more speed, the tranny shifts back into OD at 35mph and bogs the motor. This scenario happens all the time. It's a constant thing here until I get out of town. Thus, on a typical commute, there are many shifts back and forth from OD to third. I choose to leave the car in D to avoid this.
I don't see this as using up much, if any, extra gas, and it doesn't place unneccessary load on the engine. In third gear at the speeds I see in town, I may push 2000-2500 rpm. The engine likes this speed much better than the lower rpm's seen in OD. It is more efficient at these rpms and higher, and as it is more efficient, it decreases the workload felt by the engine. As far as wear, if my engine experiences excessive wear at 2000-2500 rpm, then I've got a problem.
Who knows...maybe I would see a SLIGHT increase in gas mileage by using OD in town. But I would also see increased wear on an OD band that was slipping when I bought the car. Since I have been avoiding OD in town, manually shifting the car into OD once appropriate highway speeds are reached, and manually downshifting into third when decelerating, the slip has abated.
I understand that you have a built transmission, and you have had no problems using OD in town. My transmission has been rebuilt twice (before I bought it) and is stock other than a non lock-up PI converter and a Transgo shift kit which isn't working like it was designed to.
My engine is not a dog; my transmission is a dog. That's why I've spent so much money to make it run like it should. That is why I'm purchasing the Lentech valve body...to correct problems that have been plauging me for a long time. I resent your slight to my engine, and I'll have to ask my car to forgive you as it has very sensitive feelings

.
No, I'm not full of BS, and I didn't imply that you were, either. I'm not paranoid or overly scarred. I'm simply doing what I know works and what I have had success with for three years in keeping a tired transmission running. When it goes, I'll get it built right. Until then, I have to be a sparring as possible on the OD.
If you've had success using OD in town...more power to you. I've had succes in not using it. I'm not saying your logic isn't sound. It's as sound as my logic, and I can agree with it. However, on my car, this is what works best. I've tried my best to explain myself, and I don't know what else I can say.
--nathan
__________________
'91 GT, Coast 347, 9.5:1 compression, full intake, Wolverine 1087 cam, exhaust, Keith Craft ported Windsor Jr. Irons (235 cfm intake, 195 cfm exhaust), AOD, PI 3500 converter, Lentech valve body, 3.73's (4.10's in the works), and Yokohama ES100's out back.
Daily Car: '04 Infiniti G35 Sedan 6MT