I want to optimize my braking while towing. I know most of the braking is on the front wheels. But while I am towing I have 2300lbs of pin weight and it seems I can use more rear bias on the DRW.
Does anyone use adjustable bias on their 2003 F350 trucks?

 

That's what the trailer brakes are for.

 

In a basic set-up, if pressure from the master cylinder is evenly applied to all four wheels the rears will lock first due to the weight distribution. For that reason a manual proportioning valve is used to reduce pressure to the rears. I understand you feel more braking in the rear might be better but the only way to do that is to reduce braking to the fronts. Not sounding like a good idea.

Adding a manual valve to a vehicle with ABS is dicey at best, no real way to know how it might react until you try it. I could find no reference to anyone offering tuning for the ABS system. Most in fact, are described as "self tuning". I'm not sure if that applies to our SuperDuty's or not.

If it's not braking well, there is likely a problem. Some pedal fade can be expected if the brakes get hot But it should stop firmly and evenly. If not, a thorough inspection would be a good idea.

Adjustment of the TBC is important to the overall "feel" of you rig. The factory installed TBC is quite good and integrated into the system if your truck has one.