....now my pup is doing better with the retrieve when I use his ball. Today he brought it back 4 times in a row then I put him up. It has increased over the last three weeks. From 1 to 4....so maybe in a month a couple more.
I would try another ball of the same type on a string. When he is headed back get his attention with the one on a string. How much attraction is whatever it is to get the puppy to come closer to you with the ball in his mouth. (with some it would only be showing them, with another it might mean little wiggles on the ground in front of the puppy) Then you can up the attraction with the ball on the string to encourage the youngster to drop the one he has and grab the one you have on the string. If you are fast enough, sometimes you can grab the dropped ball before he gets the one you control on the string and engage in the play again by possibly throwing it to go retrieve again. This will encourage the pup to come closer to you. Manipulation of the two balls is what you will do to get him to hold it longer or drop it faster whatever you want. Having one on a string just gives you a little more control. This works well with very young puppies who have not created a habit of the wrong behavior.
I just saw that we are working with a 7 month old puppy. The technique I described works well with very young puppies. I am not as sure about older pups as I like to imprint this early. Maybe you can change it up somewhat to suit an older faster stronger pup.