I haven't done that ever nor met anyone person that has done such a thing, so I won't pretend that I have.
First get off his back and out of any specific gear, just lunge with him, a lunge line, whip, halter, and maybe boots on his legs. First get his transitions sharp. For each gait, you will need to repeat the same steps. Add on pressure at the walk for him to go faster. When he does, release the pressure for a few seconds. When he slows down, put on the pressure again. Do not allow him to go into trot unless you ask him to do so. Gradually, you can ask him to move with more vigor and reach more with his legs. Repeat this at the trot and the canter until his gaits all have a good 'forward' to them. When you get on his back, there is another step. While establishing these forward gaits, you will have to soften him up. Do turns on the forehand and turns on the haunches and keep him from getting heavy on his shoulders by doing sharp turns and serpentines. This should be good for the arena riding. As for the trails, establish the same forward and reaching walk you did in the arena. It is absolutely key that he is not allowed to slow down until you ask him to, you want to make a forward walk the normal walk for him. Just like you wouldn't allow him to bite you, you wouldn't allow him to slow down because he wants to either (not that these situations should have a similar remedy, it is more that these are two issues that have to be fixed by consistency). Again, this is just how I would go about doing this and it may not be ideal for you.