We went from a 25' TT to a new Sandpiper 365saq 5er at 41'7". You will love the 5th wheel experience. Much easier in all respects. Hitching, pulling, unhitching, etc.
Let's assume your TT was 30' long. The box that is. So about 34 to the hitch. You are pulling 34 behind the truck. The 5er is 40'. About 3 feet is over the truck bed and about 4 feet of the included length is where your TT frame/hitch was. You are actually only pulling about an extra 3 feet behind the truck and with the pivot point in the truck bed the 5th wheel turns and backs up so much better than the TT did. They are rock solid on the road. No more swaying around if a tractor trailer passed you. In fact now with the diesel you will be passing tractor trailers even with all the extra weight back there. I went from a 1/2 ton with the TT to a 350 diesel SRW too. A world of difference. Pulls the big 5er with ease and from what I hear that 6.7 will like a breeze. I have an '08 6.4. I was having a hard time breaking 10 mpg pulling the Sandpiper. The camper is 12,800 dry and I figure about 14k loaded. I put a programmer in the truck and did gain 1 1/2 to 2 mpg pulling which is huge with a 38 gallon tank over a few hundred mile trip.
You will quickly get used to the size of the camper and be pleasantly surprised by how they maneuver. A little daunting at first by the sheer size but its a quick adjustment. At least I found this to be true. You may have to be a bit more aware of tail swing. The 365 has a 14' cantilever over the back axle to the bumper and you should be aware of that on turns.
My good friend has the Companion and loves it. Quality hitch and very easy to take in and out of the truck. I was even thinking of getting the Patriot myself. It's the same hitch that fits in standard bed rails.
As for the Sandpiper itself. We absolutely love it. Quality is good and we were lucky enough to have had no problems at all with it. It's a head turner for sure and gets alot of looks and compliments everywhere we go. There is a learning curve for sure going to units of this size. Bigger everything and more slides, electronics, tanks, monitors, plumbing, and gadgets etc but personally I love it. Never looked back.
Good luck with it and keep us informed. Tons of good info to be had on this forum specific to the sandpiper and plenty of people willing to help.
Hope this was helpful too. All the best. Enjoy.
2013 Sandpiper 365SAQ
2008 Ford F350 Super Duty
6.4L Powerstroke Long Bed CC