I only took the video. I'll let the actual owner of the K4 elaborate... 
That would be me. I have fixed the pilot truck issue, but it still does not like tight s-curves (then again, I do not think any engine does). The original owner did most of the modifications, such as new lettering (which needs to be re-done), a coal load (which could be better), the headlight, and I believe the traction tires were filed down a little, as it does not seem to have problems contacting the rails. It does slip a little due to the tight drawbar, but once it gets going, that problem is allieveiated.
The only things I have done to it are taking it apart and cleaning it, bundling the headlight wires out of the way of the drivetrain (wires used to hang in it and cause it to stall), and then re-lubed everything. I also took all of the Wheelsets (pilot, trailing, and tender) out and gave them a good cleaning (there was dirt buildup and paint overspray on some of them). I also fixed all of te binding problems of the valve gear (which had become pressed together and prone to binding). After all of that work, it runs satisfactory (for now). It is only pulling some of my passenger cars in the video, but I have had it pull more. I am just surprised it decided not to stall on the dirty joiners and switches on the layout!
I think that covers everything. Rant over...
