As Gyspy pointed out I got my east and west backwards when explaining the issue in my OP, cutting to the chase, what I meant was a slight headwind flying west from forfar to Perth showing 120mph indicated and 115 on the GPS, hang a 180 climb to 6000 and get the same airspeed but a slower ground speed,wind socks at both fields which are about 25 miles apart showed a slight westerly, I guess I am just surprised that in such a small geographical area on a very calm/stable air day with both fields being in the same long valley there was such differential in the wind between the altitudes.
I think Unusual Attitude may have explained it as that is the exact area (Glamis) where I noticed it.
Everything in MPH ( no particular reason it's just the way I roll and the Mph markings on the ASI are easier to read on my half knackered eyes)