[jclark003]

You may also want to pull the air cleaner and try to spin the compressor wheel by hand. It should spin freely. Otherwise I think the c series has a mechanical solinoid (have heard it called an "aneroid" valve). It increases fuel ratio ahead of boost to increase acceleration. If it fails or gets out of spec it can result in very poor acceleration. I would suggest you go onto boatdiesel.com, pay the $25 to become a member and do a search for "aneroid". There are several posts that describe a relatively simple test. You also may get other ideas of things to look for but I think trit21 has covered the things to check first.