Does anyone know if and when our torque converters lock up while driving in overdrive?

If they do, why the higher rpm when I turn overdrive off?

The truck has much more pull with overdrive off but with the increased rpm it must be using much more fuel.

From what I have read must people tow with overdrive on saving fuel without any problem, but there is a noticeable speed loss when climbing hills and the truck does not want to down shift unless I really step on the gas pedal. However, if I hit the overdrive off button it takes off with all kinds of power at higher rpm than if I was in overdrive when it down shifts.

Note: I am towing a 5000lbs travel trailer

 

TC should lock out in 3rd? gear? Some people can feel it like another shift point.

Turning the overdrive off locks it out of 5th gear (less than 1:1 gearing) and into a maximum of 4th gear, which should be a 1:1 ratio, hence the higher RPMs. People tell you to turn OD off on hills because frequent downshifting and gear hunting heats up the transmission and can cause it to burn up. Hitting the OD button while in 5th gear will forse a shift into 4th. You can tow with OD on as long as the tranny doesn't hunt for a gear, but it is highly advisable to lock it out by hitting the button when towing exceptionally heavy loads, and when you know that there are hills that will require a shift out of overdrive.

Ques: Does the 2004's have the TorqShift? Shouldnt' there be a Tow/Haul button, or did that start in 2005?

 

I believe the tow haul button started in 2005.

I also believe that the transmissions changed the same time. My 04 has a 4 speed 4r100 transmission.

 

Ok, so the OD lock out button will work just like that, except 4th and 3rd and not 5th and 4th.

 

I think you are mistaken about when the tranny change was made. My '03 6.0 has the 5R110 TorqShift tranny. I believe the 4R100 was last used on the '03 trucks with the 7.3 PSD. I have a Tow/Haul button in the end of the shift lever, not real obvious but it's there....

Also, I'm not real sure that the TC locks up that early. Let me describe what happens with my truck and then let me know what you think. I will start out by saying that this is what I observed while running the old General Economy tune from Spartan. I have not had a chance to play with the new tunes from the archive yet, so it may be the tuning that caused it. When I get up to 45 MPH it will shift into top gear and the TC is locked up. Engine RPM will be around 1250-1300. If I go down a hill and let it coast engine RPM stays up(TC still locked) until speed drops to below 45, then it will drop off like the TC has unlocked and uncoupled the engine from the tranny. With the stock tune, any time I let it coast it would either unlock the TC or drop out of OD(not sure which) because once I needed to speed up it would have to go through the upshift/lockup every time. That happened with the cruise on or off. That is part of why I think the tune had something to do with what I was seeing. I'll have to see how the new Maximum Economy tune works.

 

on my truck while towing my 7500lb trailer if I'm in overdrive and trying to stay at a constant speed but start loosing speed my converter locks up (feels like a shift)if that is not enough to maintain the speed then it drops to third gear.

 

That's true for the diesel, but the original poster has a V10. The V10 didn't get the TorqShift until 2005. The 2004 V10 had the four speed 4R100 and no tow/haul.

 

I don't think the Tow haul will lock out overdrive. Tow haul just changes the shift strategy. On the 4R100 OD off doesn't allow the trans to shift into OD.

 

You are correct on both counts. Tow/haul changes when the shifts happen, but all gears, including overdrive, are available. On the 4R100 all the OD OFF button does is keep the trans from shifting to overdrive.