I can only comment to the square tube Reese slider hitches. I agree with the others - lube it.
Square tube - the rollers are just rolled steel, not ball bearings. The Slider rails are also just steel. I think the rails and/or the rollers can get flat spots on them and make rolling difficult. I also believe you have to be a little aggressive (not destructive) with these heavy duty hitches to make them work correctly.
Lube the slide bars
Lube the outside of the rollers - they may slide instead of roll
Lube the inside of the rollers if they do roll
If there are indentations in the rails use sandpaper to smooth out the edges of the indentation.
Look for Figure 12. This shows the side of the legs, slider bars and rollers.
http://www.hitchpro.net/application/support/instructions/N30048.pdf