Series 60 Detroit engine issues

Hello everyone, not sure if this the right place to ask but i have a question about our 3600 S Line, and an issue we are having.

We have put a new electronic foot pedal assembly in it, but it intermittently holds high revs, and the Jake wont engage. If you pump the accellorator a couple of times it may stop, otherwise you have to shut down and start again.

Has anyone had this issue before, or can suggest what the issue is?

Hopefully this is the right place to ask. Thanks in advance...

 

Thanks for that Wrench. That was what we were starting to think, but thought I would see if anyone else has had the same issue, with possibly another solution.