Thanks for the help much appreciated!
The machine is away to work today but will be back tomorrow and get it checked
We have removed the front driveshaft to the front axle and the problem has disappeared
To me I think that the longitudinal diff is locked on causing the machine to fight with itself on good ground where grip is no issue, the steering is light compared to very heavy with the shaft connected, however I will check the trans retarder and see what it says
I might be wrong but my gut feeling points me to the drop box, however it’s only a guess