2003 c6500 3126cat allison trans swap?

[TurboDave]

I have a 2003 GMC C6500 with cat 3126 diesel.
The Allison 2400 transmission broke and customer swapped a 2200 from a 2004 f650 that had a 5.9 Cummings diesel in it.

Now vehicle goes into limp mode when it shifts to second gear.

My question is can efi live re-flash tcm with new tune for the 2200 Allison (has higher 1st gear).

[ScarabEpic22]

Can you connect to the TCM?

Try using V8 and using the Autodetect feature to see if it can read the TCM.

There's a good chance it wont work, but I honestly dont know. If you know the TCM is an AL5 or A40, it might however.