I'm sure you will get a few opinions on this, especially if some of the big-rig drivers are out there reading this.
I drove for awhile, and this is my experience and opinion (with a little fact, too).
I drove an old Ford dump truck with a Detroit Diesel, naturally aspirated. JUNK. It was gutless as all get-out! Then, I drove a '77 Kenworth with a 350 Cummins with a performance cam. What an improvement! It would certainly haul the mail, er, uh, asphault. It had I believe a Browning 10 speed. Somebody fried the transmission, so it got a used 13 speed. The Ford had an Eaton-Fuller 13 speed roadranger transmission. I didn't like the 13 speeds. However, both were either in a crap truck, or were already worn out.
Then the boss bought all-new White-GMC-Volvo trucks with 425 Cats. AWESOME!!! 80,000lbs + @ 65 mph uphill with the cruise!!! No kidding, they would GO! I liked those.
I was looking into the business about 5 years ago, but I was going to buy dump trucks, not long-haulers. This is what I had narrowed it down to. Kenworth or Peterbuilt. They had the toughest off-road, heavy duty frames I found. As far as everything else goes, it's all options. You pick which engine, transmission, dump bed (in my case), interior upgrades, etc. It'll usually depend on what your dealer will do for you at what price. Shop around.
What are you going to haul? How long will you have the truck? Lease or Buy? If I were getting one for the long haul, I would spend the extra cash and get the biggest motor I could afford, and have it tuned down to just above what your needs are. It'll last nearly forever. When my boss bought the Volvos, they were derated to avoid being burned up. And they still went 65 uphill with cruise and airconditining on.
Well, I can answer more specifc questions if you need. I did look extensively into this, although it was a few years ago.
Good luck to ya!!!
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Shane Oler
'01 2500 4X4, ETH/6 speed, ISSPRO Pyro (pre-turbo)and Boost Pillar mount, Dark Garnet/Camel, 4" exhaust (still in the box... It's freaking COLD in Oklahoma!

), Kenwood deck w/10 disc changer, NON-OEM Infiniti speakers x 4, 10 inch sub, two 150 watt amps, 20K Reese 5er hitch
Other: '70 Olds Vista Cruiser 455 (future resto project)
30' Sandpiper 5er Super Slide bunkhouse(about 10k lbs. )