OP your getting lots of ignor.....er' misinfo here from some.
One person says the Mega Cab has low gvwr numbers.
2500 truck has 10000 gvwr same as the crew cab.
3500 srw Mega has 12300 gvwr vs 3500 srw crew cab 11500 gvwr
3500 drw Mega cab has the same 14000 gvwr as a crew cab.
....or another tries to tell us the 2500 mega with coil springs isn't so good for towing.
As you see Actual owners tell us different.
Another member IB516 has a write up showing his impressions with his then new '14 2500 Ram with coil springs vs his '07 3500 srw with leaf springs towing his 37' 12k 5th wheel trailer. He posts on occasion and may make a reply for you.
Another says the Mega "eats up payload".
The Mega is 168 lbs heavier on the rear axle than a crew cab so instead of a 3840 lb payload in the bed the Mega has 168 lbs less. That means leaving the Rotty at home.
I have the same 6' 4" short bed Dodge/Cummins and pull a old '97 flat profile/square corner 32' 11200 lb 5er...and yes this combo need a slider.
As you say the new gen 5ers with the notched/rounded front corners eliminate the need for a slider.
Or you can go with a Anderson hitch...or the same style PullRite ISR Superlite series....or a Reese Sidewinder pin box setup.
Don't waste money on a slider if the combo doesn't need one