02 Tranny Problems

[dwelch44805]

I have a 2002 3500 Duramax with 180K on it. I just bought it. Had it completely serviced including the trans.
It seems to be going in and out of overdrive when cruising at speeds over 70 MPH or under a hard pull with a load. It runs fine under 70 MPH.
I've been told it is probably the torque convertor. Can anyone confirm that?
Thanks in advance for your response.

[DmaxMaverick]

T/H mode on, or off? Any power mods installed? Tire size? What is, "hard pull with a load"? How old/miles on the fuel filter? Tranny temp?

It may be normal, for the conditions and equipment. More details would be helpful. Higher speeds with heavier loads requires you to be deeper into the pedal, and this changes the tranny operation. If it were the torque converter failing, you would certainly know it. Limp mode and/or the SES comes fast when the TC slips or won't lock when it should. If you have no SES (Service Engine Soon lamp), it's probably normal for the conditions. The TCM is fairly sensitive to faults, and normally won't hesitate to scream foul when something isn't right.

[dwelch44805]

No power mods. Truck is stock all around. T/H doesn't anything over 50MPH. A hard pull is a 31 ft 5th wheel up hill or stading on it getting on the freeway at full throttle. Tranny temp doesn't change runs about 180.
Hooked a scan tool up and there are no codes. Just had the tranny serviced and all filters changed and replaced a leaking cooler.
I'm lost and appreciate your help.

[DmaxMaverick]

T/H does effect transmission performance and operation at any speed, including above 50 MPH. If you've been hauling significant loads without using it, that's probably the cause. Start using T/H with a load on, especially at higher speeds, and let the TCM relearn. If you have access to a Tech II, you can force the fast and slow relearn, which will speed up the process. If you have no P0700 DTC, your TCM is happy, and "thinks" it is working correctly.

[dwelch44805]

Thanks, I'll start using it today