Truck pulls hard to left when brakes r applied?

my brakes are not locking up...just pulls hard to left when i apply hard or moderate pressure to pedal. When i take my foot off of the pedal it goes back to normal. So they are not dragging or locked up. Will try your suggestions this weekend though to see.

Ok so we ordered all new calipers, and brakes. Got it jacked up took the tire off, and my buddy noticed it straight away...the little steel hanger thing that holds the line in place was rusty like a mofo.

He got the line loose, lessened the stranglehold the hanger had on the line, and it felt 20x better. We fussed with it a bit, worked it loose, and no more problem!

Bought all that stuff, and never opened the boxes...lol.

Turned into a $5.00 fix.

Well i kinda lied..........jacked it up and the right side tire will not spin,,,,very hard to spin....cracked open the bleeder and fluid shot out like a rocket......after i opened the bleeder it spins freely..so a new line is in order. Is that correct?