I think it's going to cost a ton. Pretty sure the first generation auto shift trans would transplant in there. It might even be possible to just convert that trans to autoshift without replacing the entire trans. Still need to use the clutch pedal to start and stop the truck. I did some googling and found a bunch of posts about converting from the autoshift to a manual. Looks like it's not a huge deal to do that. So, I would think the opposite should be true too. Here's one thing I found that might help:
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'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio