Does the SCREW have it? I ask this because I can be going up a hill on the freeway, the truck is in 4th gear (overdrive) and then downshifts into 3rd gear, now I know there is no 3 and a half gear so I turn of the overdrive and the RPMs go even higher like it shifted again!?

So what is this, I know that I am not doing 70MPH in second gear then I turn off the overdrive, so my only guess is the torque converter does not lock up when shifting back and forth up a hill at freeway speeds.

Anyone have any info on this?

 

yep, the 4r70w has a lockup clutch on the torque converter. generally you won't see the tc lockup until the truck is in 3rd or 4th gear or around 45 mph or so. and, when the tc locks up you will see a drop in rpms on the tach. also, at speed on the highway, the tc will unlock if you dip into the gas. on my truck going up a hill on say the interstate, i've noticed the tranny occasionally coming out of lockup but not actually downshifting out of overdrive. i'm not sure, but i think that locking out overdrive per the button also keeps the tc from locking up. that is supposed to help with towing...

 

dcovell
I think your close to being right on your theory. I would say while your on the interstate and the 4 to 3 downshift you feel is really the TC unlocking, then you you push the OD button it is then dropping on back to 3rd. From what I have been told a actual gear drop would be 700-1200 RPM increase while the TC unlocking will be like a 250-500 RPM increase.

 

I asume that when the TC is locked, the gas mileage will improve. If you are correct in saying it is unlocked when accelerating or towing, then is it basically like feathering a clutch so the drive line can slip a little so the engine will not lug down?

 

KY is correct. The TC will unlock whenever it sees over a certain percentage of throttle input, or at the touch of the brake.