on the 4500/5500 you have the option of the the 1000RDS series tranny (snow plow option)

I know I have a Big azz cooler and a large tranny resevior that is mounted on the firewall.

Whats Different from it and the lighter duty trucks/tranny?

RDS stands for Rough Duty Service.

I know that;) I want to know what is different inside

Internally they're the same although the RDS comes standard with the deep oil pan. The real difference is in the transmission controller, the shift parameters are different for more severe driving.