I've got a 97 ext. cab with an 8ft box, 4.6/4x4 with the off-road package (3.55 gears, approx 29 inch tires). There's about 75,000 miles on the truck, and I had the tranny flushed about 1200 miles ago. I've noticed since I purchased the truck this winter, that in highway driving (approx. 65mph) most of the time my TC isn't locking up (rpms at about 2200) however, every once and a while, it seems the TC does lock up and my rpms drop to about 1700. However, as I said, this happens rarely. For instance, last weekend I went camping, and had about 300pounds in the bed, pulling probably 1000 pounds of boat and trailer. (small alum. fishing boat). and the TC did seem to lock up on the way up. Several days later on the way back home, it never dropped down to the 1700-ish rpms the whole drive back (mostly level both ways). I know an unlocked TC tends to generate more heat, and I don't think this highway driving when it never seems to lock up is normal. I have no warning lights, etc. and around town the truck seems to drive 'normal.' Am I just paranoid, or how do I check or fix this?? TIA....

 

I wish I had an answer to your question, but i'm looking for the same answer myself. I have a 2003 4x4 with 4.6, 33 inch tires. It seems like every little hill I go up unlocks the TC, but it doesn't stay unlocked like yours seems to do. I don't remember the truck doing it when it was new, or even when I put the bigger tires on it. I think it started a while after the bigger tires. I got a Diablo chip thinking that would help, but it didn't help at all. So I wonder if it hurts to run with the TC unlocked for long periods of time? And if you do will it wear something out?

Thanks,

Marlon

 

Running with the TC unlocked creates a bunch of heat and really fast too..... I have a trans temp gauge that's installed on the trans output line and I can tell when my TC is locked or not by just looking at the gauge. I can tell by the way the rpms are running too, but the gauge is the real teller.

One quick way to tell if your TC is unlocked is if you give it a little bit of gas and the rpms rise, but your speed remains the same, your TC is probably unlocked. If you can do the same thing and your rpms do not rise and your don't really see an increase in speed your TC is probably locked.... When a TC locks and unlocks, it's almost like it's changing gears..... I can see almost a 500 rpm change from unlocked third to locked third. A little less from locked second to unlocked second. First gear is always unlocked and I've not seen where OD locks or unlocks... In OD, mine seems to always be locked, and if I give it gas, it just shifts into third....

I tow a #4500 travel trailer on a regular basis and I just leave OD off while towing it. My truck drives better and the trans temps stay lower in third as well.

You might try just resetting the computer and see if that makes any difference. Can't hurt anything, but since these transmissions are controlled by the computer, that might have something to do with your issues...

Good luck!

Mitch