I agree w/Terry the 12 cyls tend to act that way when they go into "limp" mode. Basically shuts down 6 cyls and explains rev limits. Unless you have access to alot of test equipment I'ld have it to the "stealer" or a good reputable shop equipped to diagnose. You can throw mega-bucks replacing parts only to find it was a ground or contact problem. A simple check is test your battery voltage level when it goes into rev limit mode - a low battery, especially in a 12cyl can react like this (including resetting trip meter)