I would start with small circles only at the walk. Just really go back to basics. Then as he does well and responds to the cues to stop, lengthen your line so he has more freedom. Continue at the walk. If he pulls/acts out, bring him back into a small circle.
As he continues to behave, reward with more room then start working on walk-trot transitions.
I had to do this with my boy and he was notorious at pulling away. And as a draft, I never could hold him back. Eventually I gave up on using the lunge line at all and free lunged him and that was the key for us. He does all his transitions and stop and come to the middle of the circle when asked but without the lunge line. Put a line him and he freaks out.
Congrats on the good lesson! Good feeling huh?!!
As far as finding someone with experience start by talking to your tack store. They know EVERYTHING about your local area. Tell them you are looking for someone with TB experience. Then when you get a list, interview them, ask their credentials and choose the best.
But in the meantime you can try what I mentioned above and that will at least get you guys working together. The best thing you two can do is simply be in each other's company doing NOTHING. Just hang out. Let him get to know you. Sit in the pasture and read while he's grazing or spend time brushing him and walking him.
There are other groundwork things you can do. Lunging can really sour a horse. Work on leading, stopping, backing, sidepassing, haunch turns, forehand turns all from the ground. Do short sessions with lots of reward to get some confidence in him.
Sure hope it works out!
Oh and if he's a puller - work with gloves on for awhile. Trust me!