Weird Disco question about fifth gear

[freddie1972uk]

Hi all, Has anyone come across this problem before and if yes is there any cure. I have a Disco 200 tdi and when i have been on the motorway or in fifth gear for over ten minutes or so when i go to change gear i find it very difficult to actual change gear. The gear level itself is so hard to move and even when its in netural the freeplay takes both hands to move it from side to side. eventually it goes back to normal or untill i need to go back into fifth. it only happens thou after fifth has been used for awhile.
any ideas????

[eamons 4x4]

Hi Freddie just a thought have you looked at your gearbox oil level if its to low the gears could heat up and bined then as all the bits get hot it will feel free againe.