Tom,
I had the engine in my 2000 Marquis reprogramed at the Caterpillar dealer in Texas. The engine in my coach was originally rated at 425 HP with 1450 foot pounds of torque. The reprograming increased the HP to 455 and the torque to 1550 which is the maximum rating for your engine. Caterpillar had the new engine program on line for the dealer to download, but there was a charge by Caterpillar for the download, and since my engine was out of warranty the charge was about $300. The total cost as I remember it was about $350, but that was about 8 or 9 years ago.
There are over the road programs for the C 12 that go up to 505 HP, but there are some expensive mechanical modifications that would be necessary for you engine to run that program. That is why your engine has a 455 HP max.
I liked the way that the coach drove better with the reprograming, but the change was not dramatic. The most notable was that the shift points dropped 2 to 3 MPH in normal driving. There were no adverse effects to the reprograming and I drove the coach well over 100,000 miles after the change. Was it worth the money, probably not, but I would do it again. Talk to you local Cat dealer about the current cost to help in your decision making process.
Gerald