I'll throw in another vote for upgrading the brakes on the fiver. Yes, do change fluid, and bleed the truck's brakes, but a trailer should for the most part be stopping itself. As was alluded to in an earlier post, changing to high performance rotors, calipers, pads etc brings with it cooling challenges. Not a good thing when towing down a mountain pass!
When I went from an F150 to my F250, the brakes are one of the things I was most pleased with. Granted I'm not pulling the weight you are, but mine work very well, solo or towing. Good luck