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???

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. 

Sorry, a little confused. I thought if you lowered your ball in set-up, during your approached it caused your feet to speed up thus increasing ball speed and vice versa for raising your ball in set-up.

No.  Charlest post nailed it pretty good.  Lower set up = less backswing = less speed.  Think about it.... The higher your ball drops from the forward/out position, the more momentum the weight of the ball will have to perform the pendulum bringing it back & higher into the backswing.  Thus the higher the backswing, the more momentum going forward into the release. 

Also for visual sake, picture a toddler on a swing... if you just give him a little push out he won't go as far & as fast... If you give him a bigger & higher push, he comes & goes a lot faster & the less you have to keep pushing him.

Thanks for all of the input. I was afraid it was practice, practice, practice which is costly around here but it beats being low man every week at league when I used to be the high man and I know it is my low ball speed.

I have came through this problem first hand!  I used to be rev dominant with ball speed around 13.5 to 14mph at the pins and watching my ball constantly crash the head.  I found out that my span was completely stretched causing me to have a death grip on the ball which lead to a badly muscled shot.  I would try as  hard as I could to throw harder, but would just end up hurting my arm.  Now I have a much more relaxed grip.  This combined with learning how to let my swing be "free" without muscle, I am now consistently throwing 17+ at the pins with little effort.

So check to make sure you have a relaxed grip and eliminate as much "muscle" from your swing and you will see a difference.  But muscle memory will have to be retrained.