I've got a 2017 silverado 2500 4x4 6.0 that needs a transmission. I can pick up a used trans out of a 4500 2wd van (75k miles $1750) and I'm wondering what it will take to get everything switched over to 4x4. How involved is it to change out the output shaft? I'm assuming I'll have to get it somewhere to be programmed also? A reputable transmission shop quoted $4500-5,000 if I drop it off. The truck has 250k miles on it so I am hoping to keep it budget friendly. Any input is appreciated.