Technical Diesel Cruise Control issue

[stuart rysdale]

Hi folks , I am a technician working on a lot of Ducato vans / motorhomes.. I have a van that had a replacement manual gearbox and from that point forward the cruise control has been problematic. All the switch functions work as they should , the brake pedal and clutch can also be seen in a live data read out . The only issue I can find is when viewing selected gear in live data . Starting from stationary and driving in a normal fashion the selected gear change 1 - 2 , 2- 3 , at this point some times it works all the way up to 6th sometimes there is no selected gear shown ( The Hella system just states Basic Settings at this point ) .... As long as a selected gear is shown the cruise control works . Has anybody here had experience of this ? It seems to me to be a correlation between revs and speed from 4th up but not knowing what it should be means I don't know if it's wrong . Are these correlation figures programmable using Fiat diagnosis equipment ? Sorry for the long read but I am truly stuck if you made it this far I hope you can help