After thinking about it for a while, I realized the force to move the cable carrier would be much lower if I added a spacer to the cart to increase the bend radius of the cable carrier. With Bill’s help, I made a 1 1/2″ spacer from a piece of extruded aluminum. I think the piece was a 1 1/2″ square cross section of 80/20 brand extruded aluminum framing material. This stuff is very light and very strong. We cut a 1 3/4″ inch piece of it, then drilled two holes 1 1/4″ apart for the existing bolts to pass through. I added it between the T bar and the cross bar on the cart. I had to remove the old cable ties at the ends of the cable carrier. I also had to add a couple of sections to the cable carrier, which was a nuisance because I had to remove the cable connector at the end of my encoder cable (again!) so it would fit through the cable carrier. The finished cart is shown below. You can see the spacer directly behind the red encoder. With the larger bend radius, the cable carrier moves very smoothly and the cart has no noticeable resistance due to the cable carrier anywhere along the track. I believe this problem is solved!
Cable Carrier with Spacer