I think they are C15 twin turbo CATS.
Junk..... The haul road is littered with them on any given day. They have a serious rocker arm breakage problem that Cat is not willing to address. They also get very lousy mileage when you put them to work. Up here on the haul road we work the crap out of a engine and the Cats are not up to the task. The company has been on them for the low mileage and the drivers are unhappy with the performance. Cats solution was to send up a "Driver Trainer" to teach us how to properly operate there engines to get the optimum performance and economy out of them. We all sat through there stupid class and then talked the Trainer into taking a ride up the haul road. He only went to six mile and immediately came to the conclusion that they do have a performance issue. He returned to wherever he came from and Cat sent some new software to address the issue but it was not much of a improvement.
I have not ran a Cat accert for about a year as last fall the company purchased a new 379 with a 565 C ummins in it. I have put 130,000 miles on the ISX C ummins and have not has a single problem. Many of my back-hauls are broke-down Cats. Last year when I was running the Accert Cat I had broken rockers, broken turbo bolts, major performance issues and bad fuel economy. Running the haul road I am currently getting 3.7-4.2 mpg with the 565 ISX and the 500 Cats are getting between 3.2 and 3.5. IMO the Cats are currently junk. In a year or two they may be back on top of the game but right now they have major issues. The Trainer did tell us that the new 08' generation with the particulate filter run better since they don't have much for emissions on the engine itself like the 06' model year.
By the way with only 65 more horse I can out-pull the 500 cats with over 20,000 pounds more weight. Same weight and I can pull the harder hills at over 7mph faster. 7 mph does not sound like much but when they are pulling the hills at 14 mph and I am going 21 it is a major difference in time not to mention the difference on the normal 6-7% grades. 65 horse should not make that much difference. We do not have a Dyno in the state of Alaska so Cat will not turn them up. We did send one truck to Edmonton for a Dyno run and it came in at just over 300hp so they turned it up to meet the 500hp spec but are unwilling to fix the rest unless we send them South for a dyno run