CumminZ,
I just want to toss out some more thoughts, I assume you seek a more capable truck to pull your fiver and they are out there.
The ideal truck for me (Yes Harvey, I suffer from the same thing. .

) would be an integral sleeper cab.
That gives you a rear seating/resting area and many have windows back there, independant AC/Heating systems,TV hook-ups, etc. already in place and an integral part of the factory truck package.
I would seek out a pre-EGR engine, either a Series 60 or Cat 3406 and derate it to 350 horse or so. That will provide fuel economy close to a maxxed out "B" series.
If a big engine frightens you a little both of the engine companies I would use offer very good long term warranties for a fair price, as a matter of fact CAT doesn't care how miles are on the engine as long as it is rebuilt correctly by a CAT authorized dealer.
Then you get a REAL Jake Brake to boot.
Fuller 10 speed transmission, dirt simple, easy to shift and no splitter issues that the 13 and 18 speeds will suffer from.
Singled out Meritor 40-145 rear with driver controlled axle lock. (Locks L & R axles together using a shift fork and air pressure, true locker!!) Again an integral part of the package.
You get an onboard air system and air ride, again an integral part of the truck.
You get dirt simple air brakes and spring parking brakes, again simple and parts are cheap!!!
Price out calipers and rotors for the hydraulic brake equipped non-CDL trucks that you are looking at, it is ridiculous!!!
Now regarding the M2's with fiver bodies that you see on the road,
I have seen many that are built by Freightliner and then go to Fontaine Modification Company for the addition of the cushy seats, wood grain consoles, vanity mirrors

, rear seat tv, custom bodies, pretty side fairings, the list goes on.
That is well and good if you are wealthy horse racer type dude but the rest of us will feel the pain when something goes wrong.
The pain is anything that is added at Fontaine or wherever is not an integral part of the basic truck so any foo-foo stuff costs big money and is very challenging to identify when you have an issue.
For example we had one in here a few years back for warranty and one of the many complaints was the remote door unlock only worked on every even numbered Tuesday.
Well, that was not a factory system, it was added by the body builder. That cost that guy quite a bit of extra coin to correct as we had to scramble to find wiring diagrams that were not Freightliner items, the magic box that ran it was not a Freightliner part, etc.
By the time we learned and repaired the system it incurred some additional expense with good reason.
That is why I would avoid the added stuff and go with a factory non-molested retired road tractor.
Just my opinion as a result of what I witness here at the dealer level.
Also bear in mind that I have owned Class 8 trucks and can repair them so it is no mystery that I find them to be far less bizarre than a medium duty truck.
If you have no truck experience maybe it's not a project one should attempt as Harvey says above.
It is a big step and people are going to give all kinds of ideas, thought I would jump right in... . :-laf
MIke.
