My brake controller only has settings: low, med high.
Can this be changed to a number value: 1 - 10?
Even on low setting with an empty dump trailer the tires lock up.

 

it sounds like your just talking about effort levels - Your integrated brake controller has 20 adjustments (1-10 in .5 increments) with 3 different effort levels (low, med, high) to help you control braking.
The effort levels located in the IDC under the trailer settings, and then press the + / - buttons on the brake controller itself to do the 1-10 adjustments in .5 increments to dial it in.