[lip277]

Not knowing what package you're getting, I assumed the GMC with the SL 2SA package
The 3.73 LSD (GT4) rear axle is an option (and totally required for trailering IMO)
Maybe the diesel engine covers for cold weather (V10)
I'd stick with the single alternator
Get the towing package (Z82)
Console roof with reading lamps (6C7)
Spare tire and power door locks (SAF & AU3)
Tinted windows (AJ1)
Power windows? Kind of pricey, but .... (5B5)
Outside trailering mirrors... You can get the GM ones (as part of the truck) or do the seperate ones that mount to the doors -aftermarket. Your call.
Sliding rear window - (a28)

Those are my thoughts anyway.....