Tow haul mode not working

I have done all sorts of research and haven’t found the answer

2005 Duramax/allison LLY

The tow haul button on the shifter is working/ turning the light on the dash on and off.

It seems like the shift points are changed. (Maybe)

But it won’t shift down at all when braking.

I have changed the shift/ neutral sensor on the side of trans.

My gauge cluster does not have the line under the gear to indicate what gear it is in. (Cluster has been rebuilt)

It drives just fine except it will not down shift on deceleration.

Please help oh mighty truck folk!?!?!