On my 1996 3500 4x4 with the V10 I am having a problem with the trans not downshifting with the OD OFF while towing and pulling a grade. Actually, it seems the problem is the torque convertor is not unlocking which will allow a downshift. It works fine with OD ON, and unlocks and downshifts when it should, but when I lock it out, no downshifts, and occasionally, it will act like its trying to unlock or downshift, but its almost like its cycling between locked and unclocked at that point, and still no downshift until I turn OD back on.
On the big grades, the convertor will not unlock and no downshift occurs and the speed will drop off pretty far, then I will hit the OD back on, and a downshift and I'm right back up to speed. I've checked the adjustment of the Throttle valve cable which is ok, so I'm thinking the torque control convertor solenoid (TCC) , but the same solenoid controls both the 3rd and 4th gear clutches, depending on the OD on or off so if the solenoid is working for one shouldn't it work for both or am I missing something?
The vehicle has 78,000 miles on it and has been serviced since new every 20K with Mopar fluid and filters, and this issue occured before and after a dealer 100% fluid exchange and band adjust. The first time it occurred, I wasn't sure about the no unlock, but on my last trip, I was on the freeways thru the Sierras where it was pretty obvious what was going on. Other than this issue, it shifts fine and seems ok.
Thanks for any suggestions.

 

Check TV cable adjustment......