3rd to 1st Violent Shift

[CGWaterfowl]

I have a 2014 3500 Longhorn with a 6.7 L6, 68RFE that has been in the shop for a year with no end in site. HELP!
So the problem is that when I come to a complete stop the transmission will shift from 3rd to 1st very hard. To the point I literally thought I got rear-ended.
I took it to a transmission shop because I was 23,000 miles outside of my warranty (123,000 miles on the truck) and couldn't afford the dealership prices to "repair".
The transmission shop put in three different rebuilt transmissions, a new ECM and shifting cable. Still the issue remains.
They gave up on it after 9 months and now it is at the dealership.
The dealership is telling me that I need to choose what they should do and my options are a new sprag or a new ECM. Both of which the transmission shop has done.
The dealership is saying I need to choose because if the problem is not fixed I am still held responsible for cost.
Has anyone had the shifting issue before? I can't be the only one to experience this...
Please Help!

 

[Sandevino]

Is tow / haul mode on?

The 68RFE will shift firmly (I.e.: no slipping) compared to other transmissions. Any codes? Is the valve body new? Fluid level and color?

 

[CGWaterfowl]

Tow/Haul mode is off and hardly used.
I understand the 68RFE has a bit harder shifting but the shift from 3rd to 1st is extremely hard. It literally feels as if I was rear-ended.
It does continue to put out the same code. Error Code P0731, gear 1 Incorrect Ratio.
The fluid is new and clean, changed with each new rebuild put in.
Three new valve bodies put in.

 

[Sandevino]

Let me get this straight...

THREE different transmissions - I presume used or rebuilt?

We’re the shift solenoids replaced?

Same for the TCM - swapped with used or rebuilt, if at all?

If all the previous check out, what does the transmission speed sensor look like? Wires good? Has this been replaced?

I’ve seen too many 68RFE issues chased down over the speed sensor.

Check and report back...

 

[CGWaterfowl]

The images are the receipts of work done. The shift cable was also done but can't find the paperwork on it.