Auto Locking Diff. on Dodge trucks questions

I am looking at 1 ton flat bed trucks for me farm work lately. I noticed the local car dealer has 3 '09 Dodge 3500 4x4 flat beds for sale. No chevies but has one OLD Ford F350 heavy duty that may or may not be a 4x4 (they has the wrong paper work on ze windows)
Thing is I want a Chevy because of that Auto Locking differential (bad experience with a Ram 1500 4x4, limited slip diff's SUCK!!) but they have the sticker price at 25k for these trucks and so I am wondering if there are strong auto Locking Differentials I can put in or have put in that truck? Are there OEM Auto locking diffs from Dodge? Are there any Aftermarket auto locking diff's that are as strong or better than OEM stuff out there?

Sarge

Correction: They call them "chassis cabs" and they have 1 white and 1 black, both reg cab sized (doesn't matter for my needs)

Thanks,
I spent about an hour looking for Differentials on Google and came up with jcwhitney crap Stupid bots!!!!
And I could not find a one that would fit my Dodge or that was not a limited slip! I hate limited slip's they are a crock!!