I just had the transmission gone through, using sonax parts and a billet triple disk converter.
I started into the transmission because I wanted to do the mods for 2nd gear lockup. I tow on some pretty steep grades and 2nd gear slush up hill made a ton of heat, and coming down, 3rd was too high to give me effective exhaust braking.
I have towed with the truck, using a pacbrake and a lockup switch or controller with no issues for a couple of years. I could always get 3rd and 4th lock for the brake.
After this rebuild, it won't hold 3rd lock when I let off the throttle. It tries to, it drops about 500 RPM but not all the way down to idle. I can flip the lock switch off and it will drop that last bit quickly, say from 1250 to 1000.
It seems to not have enough pressure when the throttle is let out to hold fully, so I tightened up the TV cable and drove it some more.
Still no lock.
4th gear lock is rock solid, up or down. Any normal acceleration lock is rock solid. It now locks in manual 2nd under load if I flip the switch. It just won't hold in 3rd any more, or 2nd when foot is off the throttle. Anybody have a suggestion?

 

Personally I'd take it back to the shop that rebuilt it. Where are you located?

 

I did. They are still trying to figure it out before they take it apart again. I was hoping somebody would have that little tidbit of info.

 

It sounds like they aren't extremely knowledgeable about the 47RE trans.