Barn-Sour and Rein-Problem horse?

If i'm riding in the pasture, walking is OK. It's when i'm trotting and loping. Trotting is some difficulty turning and keeping straight; it's loping that's the HUGE problem. He can't go 5 seconds loping and going straight without turning around and going full-blast gallop back home. I never let him win with that-I pull real hard back on the reins (because he won't respond just normally pulling back while going fast) and after a few seconds he'll stop. Another thing for turning. If I just pull normally to turn (this happens when I'm sometimes trotting; always loping or accidental galloping), his head will turn, but not the rest of his body! It's weird! He'll just keep going straight with his head to the side. After like 6-10 seconds he'll finally do it (most of the time) HE WON'T TURN WHEN I ASK, BUT WHEN I DON'T ASK TO TURN, HE DOES IT!!! AND I'VE NEVER SEEN HIM GO STRAIGHT-HE ALWAYS TURNS! Please help.