So i occasionally pull 25k. Trailer brakes suck so this is usually just a short move for the skidsteers but when im really getting on the brakes, the truck is yanking left. Thinking air in the line but not sure. Any suggestions? Thanks for any help. This is my first post on the site.
04 f350 KR FX4
225k miles

 

Sounds like you need to go over the trailer brakes (adjust or replace) and make sure the brake controller is working properly.
As for the truck, it could be air or a sticking caliber, if it's pulling to the left the right side isn,t working properly. At 225k miles unless it's been done I'd replace both front calibers and use to highest quality pads I could find.
Your at my upper limit that I haul as well, my F-450 has bigger brakes than 350's have and my trailer brakes are in good shape, it'll stop a little faster than a loaded semi and that's a pretty good comparison in brake size to weight ratio.

 

I'm suspecting that the drivers hub may be causing it. Put brand new severe duty pads and new rotors as well as a passengers side hub a couple weeks ago. Calipers were replaced mid last year (+-20k miles) as well as the ps hub. Seem to be tearing up hubs for some reason. Ds hub had a little play. Boss paid for parts since I tow his equipment, just didnt wanna break the bank on him. Guess I need that hub and we'll see

 

As far as the trailer, I'm ordering some brakes asap, already adjusted and can only get 2 wheels to grab slightly. Tired of puckering up coming down bridges. Also, I rarely pull both machines. But 1 and attachments weigh about 15k plus the 30' gooseneck. Probably close 35k with truck and 100gl fuel cell full plus tools and misc BS

 

Replace the brake lines from the caliper to the frame, I've had them go bad and it acts just like a stuck caliper.
Had my front axle down for a gear change a couple months ago, front hubs had less than 5K miles and the right one was rough when I rolled it, got another hub.
New parts are 50/50 junk nowadays.