I drive an 05 T600 with 1.5 million miles on her and one rebuild under her belt and she’s fine, absolute reliability compared to the new engines and all their ills. We still have a 97 on the road, two 99s an 03, three 05s and six 07s that are all pre emissions for all intenses and purposes with the 05s and 07s being CAT C15 acert engines with no EGR valve. We also have 3 Cascadias 2014 and newer that whilst not bad, give more trouble than the rest of the older trucks combined.
One of the 99s went from New Brunswick to Florida and then to BC the other week. Our company maintain them meticulously and they just keep running. I’d prefer a bigger modern truck for living comfort but the most important thing for me is reliability and not being stuck for days on end in a dealer on no pay etc.