I have driven quite a few FreightLiner trucks in my day ranging from FL60, FL70 & the FL80
Currently I own a 2000 FL80 with 210HP 3126 and 6SPD Fuller trans, Aside from the door air leaks The truk is solid, has alomst 485k and still runs strong, the interior does not rattle the dash does not peel, its starts right up, It had the orginal clutch until 450k and I had the tyop redone after she threw the #6 Vavle.
Bottom line is Change the oil every 7500 miles, dont beat on it 2much, I hardly rev the motor past 2000 RPM unless its in 6th gear and cruiseing at about 75-80 MPH, I get the blinking engine light at 2300 RPM than the fuel cutoff kicks in at 2400 RPM. You just cant beat on these trucks, like anything else treat them right and most likely they will treat you right, There are lots of these trucks out there forsale that have been used for expediting and are mostly highway miles that carried very little weight, so, they may cost a little more than a non expedite truck, but chances are the non experidter truck has been driven hard by more than one driver on a daily basis and carried lots of weight.
Overall if you can findone you like and can get some service history on it, its a good bye, I got half a book of service history on mine when I bought it.
Good luck.