I have a tundra pulling a TT same weight as yours, and I use a P2 instead of a P3.
After the brake shoes are worn in, I set the gain at 9.5-10 and normally do not use any boost. If we are in the mountains I will go up to B1, but rarely on the flats.
I have felt some grab when applying brakes from 5-10 MPH like in traffic but it has been that way since new.
Mine has Lippert axles and "self-adjusting" brakes that adjust with each forward stop. I have found that the grabbing gets worse the more stop-and-go traffic I have to endure.
When new, also had trouble with one single wheel continually adjusting itself too tight. Finally took it apart and discovered the wire cable that participates in the automatic adjustment was twisted a couple of times and thus effectively a little short. Straightened that out and no problems since