Assuming you have the integrated brake controller, the way it works is based on how much brake pressure you apply as well as how fast you are going. When sitting still, very little if any braking will be applied to the trailer, only the manual override will apply full braking. It is not like pendulum type controllers that adjust current based on the g forces applied to the pendulum. On those controllers they will ramp up until full power is applied.
So with that said, how and when are you testing the braking? If following standard pre-trip procedures, you apply the trailer brakes via the dash control and not the pedal, trailer stops both. If you are slowly rolling and apply by the pedal, then the truck does the actual braking, which is normal since not enough speed is detected in order to apply the trailer brake though the IBC. OTH if you are at 10 and slowing from 40 MPH and it feel as though the trailer isn't doing anything, you may want to have the truck checked out. If there is trailer wiring issues, neither the IBC or dash controls would apply the brakes. They both use the same wires, the dash controls are the override. You can also verify with the dash controls the variable braking, it is not an on/off switch, but if you squeeze it just a little then a little power is applied, When fully engaged it is gain 10, irregardless of the dash settings. Your trailer should fully stop with normal braking at the 8 gain setting. After towing several different trailers with my trucks, 8 seems to be the best setting.