Okay, well... I had a jumping lesson few days ago... It was quite awfull I just couldn't jump that evil evil triple combination correctly... :/ I did it only from 3rd try... So, although I look baaad, I decided to put the video here and get some advice on how to look goooood
I see that you need to release just a little more. For the speed your going, you can still hold a little, but just a tiny bit more follow is in order.
Bring your shoulders back - you are hunching them just a bit over the jumps. I would ride around in two point for as much of the ride as you can. Just stay there, in two point, during your flat. Make sure your trainer says you look good, and just stay there, in that position. This will help muscle memory, and help you get better strength in all areas.
Do you go to the gym? Do you do any sort of workout? I heavily reccommend it. Core work, leg work, is what I do. I might only do it 3 times a week now, but before I did those workouts every day of the week (not weekends,) and it has really done a lot of good to my riding!