Maybe you should let him canter to the jump. Its easier for them to jump from a canter than a trot especially if the jump isnt a small one.
If he's rushing because he's nervous or unconfident it might be an idea to take him to basics and get his confidence going over some trot poles and small cross bars. Failing that, try circling him and not going over the jump when he rushes. Circle him until he calms down and then approach them jump again. Repeat if necessary ;)
Some horses will just pick up speed a few paces before a jump. My wb canters up the jump quite sensible and then about 3 strides away he ups the speed and the length of his stride so that 3 strides becomes 2 then calms after the jump. That's just him :) whereas my mare keeps the same pace no matter what. She's not a rusher. She prefers to size up the jump, think about and then cruise over as delicately as possible :) she's such a princess
:roll: anyways my point is that different horses deal with jumping in different ways. As long as he is collected and facing each jump with confidence it shouldnt be too much of an issue. If he is rushing the jump and not thinking though that is something you need to deal with using those methods I've mentioned and other methods im sure other people will have for you