Without seeing a pic, it likely is brake wires, maybe damaged from blowout. If so, they need to be reconnected so the brakes will operate. There are several easy ways to test the brake operation of each wheel.
As to the sagging 250, most 250s sit level when empty, due to only having a 2" block under the springs. So with a load on the rear axle, it can appear to be sagging more than a 350, which has a 4" inch block to raise bed higher than level, when empty. You could change to the 4" blocks, or use bags to level, if needed. Your right, it is great to tow a FW level, rather than nose-high.
Jerry
