Not a Z71

I've been looking for one for my 2018 Custom 4X4 Crew Cab. Every thing I look up on the internet says it won't fit my truck. I haven't even found out what size my rear diff is or the gear ratio. I've heard some say you have to go with 411 gears. Didn't want to do all that, just put in a Truetrac in the rear. Do you know any part numbers for one? Thanks!