GQ 4.2 petrol Auto 4th gear ISSUES

Hey Guys. I have an issue with the 4th gear. It still drives fine but just won't change up, Any ideas?

Thanks in Advance :)

This may be a silly question but is your overdrive turned on or off? Or is the power / auto / hold switch set to Hold?

Could be a range of things and is a matter of elimination.

I assume you mean the torque converter isn't locking?

I have also moved your thread into the gearbox section.