I have a 2002 SE V-6. When climbing a moderate grade, if I switch the overdrive off, and then switch it back on, the overdrive does not kick back in. Instead, the engine (maybe drivetrain) noise increases a somewhat, and it won't upshift until I back off of the throttle (I am not flooring it).

Has anybody else run into the same thing?

Mine does the same...i usually click into third gear (O/D off) when climbing any hills that needs more gas since i would rather run a few hundred higher rpm's then applying more gas. you can really notice sometimes when going around 45 mph and the xterra downshifts between 4th and 3rd but not fully 3rd...i think it has something to do with the torque converter and then you start to feel the need to apply more gas but by just clicking into 3rd (O/D off) it can give you a good shot of power.

You're sort of "tricking" the automatic tranny. The overdrive will lower your RPMs by about 1,000 for highway driving - which gives you greater mileage. By clicking it off, you effectively drop into a lower gear. If you're applying the gas when it does this, it will stay in that lower gear up to a certain shift point/speed.

This is completely normal, and the way an automatic tranny works...

Good to see someone else that has some idea what's going on LJ. You're pretty much right. We've come a long way since 12/00 on the Yahoo clubhouse when we were talking about the torque converter LJ, the "shift" you mention that's "not quite to third" is just the TC unlocking still in 4th. Turning off the OD locks out 4th, forcing you into 3rd where it's almost impossible to have the TC unlocked.

What Ecks is experiencing is 3-unlocked, and about the only time you will experience it is after turning the OD back on while still under load. A quick off-on of the gas will let it shift on to 4-unlocked, and as long as you're not asking for much it should settle into 4-locked.

Brent

plus, the TC lock does not operate under ~50 mph in any case.

Brent...is what you're talking about what I feel as though is a 5th gear in my auto? When I have OD on, after cruising with no load my rpms drop real low, then if I step on the gas it kicks up about 1000. Then when I hit the turbo (OD off) button it goes up another gear. It almost feels as though overdrive has 2 gears and then od off is 4th gear. What speed/ rpm is 2nd gear on an '03 SC X good for? In other words, whats the maximum speed I can be travelling and toss it into 2nd gear for a BIG power boost?

Yup, that "2 gears in ovedrive" is the difference between the converter being locked and unlocked.
As for second gear, I don't know what the max speed is, but if you put the selector in "2" and accelerate while watching your RPMs, about the point you reach the redline is it. I don't recommend it though, let 3rd do the work. I've knocked it down to "2" a couple of times when I wasn't paying enough attention to my speed and instantly hit the rev limiter, not fun.

Brent

I'm just disappointed with 3rd...it seems very doggish after 4000 rpms if you are accelerating out of 4th. When I pulled out the other day form a stop, I tried to manual shift the auto...left it in 2 and 1st gear (which is perfect power) carried me to about 5400 rpms...being that I had it in 2, it rose again to redline and I then put it in D with OD off and man it really had tranny shif lag, but it was much better than upshifting. I was up to 70 mph in no time. I was just wondering what the max speed is, because sometimes, just upping to 3rd is not enough balls to get by someone in a hurry.

Edit: Oh yeah...it is strange that when I have the tranny in OD and it kicks up a gear for heavy acceleration...it gets stuck out of OD!! I was needing to get by a truck on the highway the other day and rode it up to 80 mph in 3rd....then the RPMs stayed at 4000 and it would not shift back into OD until there was no load on the engine at all...guess it was getting too hot???

Leave O/D off until you can back off the throttle. There's no need to wail in 3-unlocked!

Brent