Retraining - bolting issue

Question
Hello Dorothy,
I would like to thank you kindly for reading my question &  responding.
I'm taking care of a 7 year old gelding arab, for a friend.
She has raised it since 3 weeks of age (She was 14 at the time)... She has been around horses for most of her life, and with this horse (Trinity), she was the one who trained and broke him.  She has identified that one of her errors, when he was younger - when she first began to ride him, was to get on him and let him run for the first stretch of the trail ride - usually uphill, to get the energy out of him.  I've substituted the round-pen for the warm up.  But when we are out on the trail and I've tried to get him to trot - he just wants to bolt (gallop) and gets frustrated when I hold him back.
He's a wonderful kind, trusting personality, and is very willing when I work him on the ground.  I would appreciate some guidance as to what steps I can take to teach him to come down a couple of notches and be willing to work on my speed levels instead of his.  
My friend didn't realize it was a problem, until I took him on - as she's 22 y.o. and fearless, and I'm 50 and more conservative...
Does it sound to you like we need a professional trainer?
Here's what I was thinking I need to do.
Work in the round-pen on ground manners, changing directions, and releasing energy.
Work in pen - reiterating the walk - trot - canter transitions (on the lunge line).
Ride horse in pen on walk & trot & walk transitions - until solid on response.
Ride horse in pen on walk, trot, canter, trot, walk transitions until solid on response.
Work on the trail as in pen.

When he does walk on the trail - he is a delight to ride, not spooked easily, and has great potential.
The thought I had was - we have a trail (hill) that is about 2 miles long.
I thought after the round pen training - to walk him to the bottom of this hill and walk him up - to remind him, it is at my pace, not his.
Then repeat, but this time walk - trot - walk up the hill.
Depending on his response - repeat and do walk - trot - slow canter - trot - walk.  (This would be the equivalent of 12 miles if I did 3 cycles... would the tiring the horse help as part of the training / attention?)
Again, I'd like to thank you in advance for your response.

Answer
Hello Jacqueline,

The lunge line need not be 60 feet long.  30' to 35' is long enough to give you the large circle.  (it will have a diameter of 60')

10 minutes each way on lunge is good before changing directions. Give at least 2 minutes rest at walk after each 5 minutes of trot.

As soon as you feel safe, do away with the lunge warm up and take him for a walk instead.

Good luck,
Dorothy