On a Colorado there is a common issue with the rack mounting bushes. These wear and allow the whole rack to move side to side when steering. This is all movement that SHOULD go into steering input. Clearly Mark's ball joint is stuffed there and needs doing, but you need to check the mountings too. The bug nut shown in the video relates to a pre load of sorts and doesn't typically seem to need a deal of adjustment. With no other obvious play, get someone to rock the steering wheel back and forth with the wheels on the ground and the engine off. You will be able to see if the whole rack is sliding back and forth in its bushes. Any more than a few mm and it should be an MOT failure.
When mine went, it was a very new problem and even Toyota didn't seem to have seen it before. I had Milner rebush my rack for me (I did say it was a long time ago) and that cost me £50. But the difference it made was huge. People have since done the same repair and had good results. Made easier if you have a decent workshop and you're not scrabbling around on the drive.
That little torque gauge is nice and I happen to know that Trevor at Freedom 4x4 has one. They are very expensive. Might be worth you asking Trev to have a look. He's pretty close to you.
