Kgmz is spot on in his summary of the TK Commercial series. Generally speaking, the highest position on that trl should be plenty for normal travel. Entering a job site you can raise it and let the Hyd support it to get over a hump or some rough ground. Also, there is a raise and lower valve on the back, or there should be, for the air-ride. That will gain ya a little bit of height.
On the TK Advantage trl, if you look there are 2 position that come from the factory. The large door is the low position, and then there is another "door" that is hinged that you can flip up to gain some height. That second door is about a 1" shim. I have a TK130 that has that system. I had TK shear off two additional shims that are 1/2 x3/4xthe length of the existing "door", and since then have added another size shim that is 2"x1"x the lenght of the "door". Those extra shims allow me to run the deck on the highway without riding against the hydraulics with plenty of underclearance. One downfall is when you have all the shim in place, you change the 5th wheel angle enough for it to be a concern if you were to drive into a steep incline, like a driveway, etc. Ya just have to keep that in mind. It also allows for lowering the air ride down at the back in an instance where you have a load that is over heighth at the rear of the load. Helps to keep from "touching down" while on the highway, like from the bounce when entering and leaving a bridge. I have pulled the other style trailer, but would prefer mine over it regarding the hyd neck styles.
Rigandig