When I started working in the RV business, I was taught that electric brakes on new trailers won't always lock the trailer tires on pavement, some will, some won't.
Unlike autos, trailers sit around and the inside of the drums rust just like the outside, especially in humid areas like Florida. This winds up putting a coating of iron oxide powder on the braking surface of the drum and reduces its friction until it burns out.
You don't say how much usage your new brakes have, but new trailer brakes are like new car brakes... it takes time for them to wear into each other and the new linings to be burnished. You may not have turned the drums, but did an earlier owner? If the drum diameter has been increased, there will be less contact area with the drum until the lining curvature has worn to fit it. In the old days, I had car linings arced to fit the drums after turning.
We adjusted brake controllers on a packed clay road, where it was easier to slide the tires, with two guys watching the truck and trailer wheels, and adjusted until the trailer tires just slid first. Then we did it again with a guy on each side to make sure both sides of the trailer were skidding at about the same time.
That's what's important as far as adjustment. I know a lot of folks want maximum braking and adjust the controller to be just short of lockup on pavement at full braking, but even with the Kelsey Hayes hydraulic controllers, this often lead to the trailer overbraking and pulling hard on the tow vehicle under normal situations.
Another problem with the trailer braking signifcantly more than the tow vehicle is that the drum brakes don't shed heat nearly as well as the discs on the tow vehicle, so it's important the trailer doesn't brake any more than necessary to keep slight tension on the truck, especially on long downhill grades.
13 amps sounds plenty for 4 brakes. That should tell you that you don't have brakes on one side accidentally wired in series (which would lower the current) rather than parallel, and that the controller and the wiring in both the truck and the trailer is doing its job. If the brakes really have some mileage on them and are past break-in, I'd probably take a meter to them just to check.
I wouldn't have worried about the controller since you were getting that much amperage. But Jordan's concientious enough to want to check it on another meter. BTW, if you ever change vehicles, send it back to him and he'll replace the cable at no charge.
Here's a link with some good info and troubleshooting.
Hope this helps,