Outer Limits 4x4 Board

I have a 92 HZJ75 diesel cruiser ute with a manual gearbox.

It lives outside & never sees shelter (after all it is a work truck)

On cold mornings the speed displayed will be out by a factor of 6ish. IE it will pull 100km/h in 1st, & 180 in 2nd.!!!!

It is completely linear, ie if you slowly speed up it slowly increases the speed it displays. If you slow down it reduces the speed displayed.

This will happen for 10-15mins on some mornings & then display normally, however it happened for 100km of city driving yesterday, so I am getting concerned it is getting worse.

Anyone had a similar experiance or know of a solution???

Is is electronic or cable drivin

I electronic was thikin maybe moisture mite be the prob

just an idea dont shoot me

Speedo head or the speedo cable is about to break look for a bend in the outer. If no bend it maybe the speedo head keep driving till one stops working .