I have a 2000 model c6500 I just bought. It has the 3126 Cat in it and a 5 speed spicer I believe. It's been at mhc getting checked over and they come to the conclusion that the speedometer not working is the reason it wont go past 17-1800 rpm in any gear. Has anyone else ever had a problem like this? It isn't throwing a cel until it hits the cut off and then it just flashes and goes away. It is almost like hitting a governor. Runs great and starts to build boost until it hits also. Any help is greatly appreciated. I have searched and couldn't find anyone else having the same issue. Thanks!

 

Do you get any codes?, if it flashes, it should store a code.
Just from what you have described, it sounds to be normal, if you are reaching 1800 rpms that isa little low, what series do you have, (b, e, etc)
More info would help
Is the cluster reading correctly?
When is the last time it had an oil change, is your oil level on the stick correct (showing full)
These are run off of oil pressure.