Is a new Clutch Cable required?

[Mack 6]

Hi Guys.

After being run hard over a weekend long hillclimb event (and one clutch burning burnout by "matty31") I have lost a bit of clutch functionality, and whilst I'm presuming its a cable, I'm open to suggestions.

It's an AU6 with T5Z setup for a 6 with a HD extreme clutch (900kg I believe)

Originally it was a struggle to get into gear sometimes, even with the clutch pushed all the way to the floor, so decision was made to readjust the nut on the firewall where the clutch cable comes through. (no, the firewall isn't cracked)

It took a bit of adjustment before the gear changes cleared up, but then the clutch slippage started occuring. After a fair bit of test and adjust, I am still at the point wwhere gear changes require clutch all the way in and a bit of effort, but I still believe it's slipping a little bit.
The nut is about 1-1.5 cm toward the cab from it's original position, so i am thinking the throwout bearing is sticking (hope not) or just the cable is stretching (a quick and easy solution).

Any advice would be appreciated.