I have tried backing up on the approach but I end up stopping way behind the foul line.
I have tried raising my ball in my set up but has not helped much.
I have tried speeding up my feet but am having timing trouble with that.
I have tried making my backswing a lot higher but must be slowing the ball down during the forward swing.
Does anyone have any other ideas other than just practice one of these until it works???
Those all work, but I'm not sure how much time you spent on any one of them.
What I'm thinking when I see you write such as this, is that you may not have spent a lot of time on any one of them or maybe, better, enough time and focus.
They all can and have helped a lot of people increase their ball speed and they are proven techniques. WHat I suspect is also happening on some of them is that you are not allowing your body to react as it would naturally but are subconsciously forcing it to stay in whatever mode you have been using for all the years you have been bowling.
For example, the stand further back approach, where you say you wind up further behind the foul line. If you allowed your body to do what it wants to do, get all the way to the foul line, you'd find that you took not only longer steps, but faster steps. Both would increase your ball speed, from a little to a lot. If you used a higher pushaway, together with the longer steps, it would produce a higher backswing, which if you allowed it, would produce slightly more ball speed.
These techniques work if you allow them to work. It's human nature to try to force your body to do what it has always done. Kind of like a forced or controlled armswing: in order to allow an unforced one, you have to relax both your "mental grip" on your muscles and allow the arm to swing as much as it naturally wants to swing. By engaging your shoulder muscles you are forcing your body to control the armswing and its height.
In your lengthened approach, you are forcing your legs/feet to take small steps, just like you always have. You have to let them go, relax and let them take you to the foul line.
Your mind subconsciously refuses to let go of its super-control of your body. You have to let go, relax. No two ways about it.