03 LB7 dropping out of Overdrive

[brownstone]

Hi all
I have recently run into a problem with my 03 Sierra D/A. When driving in overdrive the transmission will simply drop out of gear for a second. Its like all of a sudden the engine has no load on it and the rpms spike up. I let off immediately and a few seconds later it seems to lock back in and you can go again (it does not shift down again, it just locks back into 5th gear). This is happening with very little load on the tranny, and is happening more and more frequently. I suspect it either overdrive clutch pack, torque converter, or a sensor of some sort. When I drive in tow mode the problem does not happen.

03 Duramax Crew Cab
4 inch Turbo back MBRP exaust
Predator programmer (run on stock mode most of the time and never on high tune)
AFE intake

Truck has done very little towing and hasn't been towing for the last 3-4 months.

If I have to drop the tranny to get it fixed any ideas on what else I should do? should I upgrade the torque converter or put in a better shift kit?

Thanks
Stephen

[Mark Rinker]

Observation - (but not an explanation)

Since the problem only happens when NOT in tow/haul it would appear that it may have something to do with the torque converter?

T/H causes the torque converter to lock 1:1 earlier (slower) and stay locked during towing cruise.

Good luck.

[brownstone]

The problem has now started to appear when in Tow mode, so then I turned off the overdrive and even started to do it in that mode. Dropped it off at the Dealership yesterday afternoon, and their diagnosis is that the Transfer Case is ruined. Funny thing is, I had it at the shop two days ago to get the output shaft seal replaced.....

[Mark Rinker]

Hmmm...this should be interesting!

[brownstone]

Well I now have a new transfer case. I wish I had more time to deal with this repair but I'm out working and I needed the truck back ASAP. The repair bill was just over 3 grande so I feel like I've been beat up and taken advantage of. But the truck does seem to be shifting normal and its back on the payroll so that is the main thing.