Hi Folks,
Thanks to all that have posted. I also had this issue and in my case it was the boost sender unit (black box just behind the right shock absorber tunnel). To fix it, I opened up the case then just reflowed (just melted the existing solder) on all 3 of the pins that make up the external connector. It should be pretty obvious which ones they are cause they are the biggest. I couldn't see any hint of a dry joint but it is possible it was really fine?!
Anyway, since reflowing those pins the gauge has worked perfectly
HTH
Andrew