K3 has everything you mentioned. I had the MM chassis in my last unit, nice unit and it ran well. 450 will make any moutain climb just have momentum on your side. If you get behind a 18 wheeler going slow and you slow down your rig will not recover and you speed will decrease. Went to the K3 and there is a difference. I will mention the obvious differences but you have to drive one for awhile to appreciate it. Some of the differences.
Disc brakes at every wheel much shorter stopping distance
16600 front IFS with 9.5 rims all around
3 stage brakes (you better have your seat belt on when you engage 3 level)
Hadley air ride system and leveling (system operates as you drive) and levels the road as well as prevents the feelling of top heavy. Experienced some high winds and had no issues with getting blown around
Hadley system also allows you to raise the coach 4 inches in the front or back or the entire coach. It also allows you to drop the coach 4 inches in the same fashion. The raising comes in handy when you need ground clearance in some parks or roads.
Allison 4000 trans (different gear ratio than 3000)
450 hp has 488 gear ratio K3 has 373 ratio ( you tack about 450 rpms less than a 450. Engine works less saves diesel. I tach about 1450 rpms at 65MPH
you will gain about 3 inches in height in the cargo area
K3 radiator fan is a direct drive .
When leveled on the hadley air system (no jacks down) the k3 does not shake or move as much as a MM chassis when the jacks are up. I rarely put the jacks down, I just pull into my site press the hadley leveling system the cornerstone takes over and levels the coach.
I hope that gives you an idea of the differences. Both units are great, owning both and driving both in various situations, there is a measureable difference k2 vs k3 in ride, handling and functionality. I hope that helps you.
Lisa & Mike