Oh, boy . . ..
Multiple issues here, and trust me . . . I've been there, done that, and buried the shirt.
Issues - in no specific order:
(1) Make sure the brakes on the trailer are properly adjusted and functioning (just because they're new doesn't mean diddley!!);
(2) Yes, some braking cycles will be required for optimum pad to drum contact - 50 hard stops?? Hmmm??
(3) What controller are you using? Many of the "budget" controllers just don't have the guts to pull down a heavy trailer. I happen to be partial to the Tekonsha Prodigy (although there is a "newer, better" unit out from them). It will haul down my 17K# race car trailer with authority. Which is more than I can say about the previous 2 controllers I had, which both darn near got me killed!!
(4) Very important!! Make sure the wiring to the brakes from the controller is heavy enough (8 gauge is smallisn, IMHO) to handle the current, and that both your hot and ground connections are good.
(5) You may NOT have (or want) enough braking to lock up the wheels at speed on pavement. You should however, be able to manually apply full braking and slide all 4 (6?) wheels on gravel - easily.
Hope this helps!
Norm & Janet
FMCA; WIT; FCOA; Good Sam; Passport