This is not a feed problem. But, unless he is thin, he does not need much if any concentrate. A good free choice loose mineral will give him what he needs.
There are two common denominators on this horse and his sire both being 'stubborn'. They had the same genetics but more importantly, they had the same owners / handlers.
Some horses are bred and born a lot less willing. Very few are born 'stubborn'. Most stubborn horses have found there is a 'pay-off' for arguing with their handlers or riders. This comes from inconsistent handling, unclear boundaries, and 'pecking' and 'nagging' at them when they do something wrong.
Less than willing horses must have very clear boundaries, can never even think they have won for 1 second and should think they are going to die if they do something aggressive -- anything aggressive.
To nag and peck and not get the proper end result only emboldens them and they get worse and worse. Some horses are a lot less dominant by nature and a lot more forgiving. They cut people a lot of slack, but they can still get spoiled.
A couple of years ago I had a lady call and ask about a gentle, well-trained trail horse. She said she had a horse that was mean and she was afraid of him. I had her come and bring her horse with her. It turned out this was the 3rd horse she had bought over 5 or 6 years and all three were 'stubborn and mean'. All had been easy to ride when she bought them. She owned ALL of this horse's problems and probably the ones before this one. I told her I would not sell her a horse if she did not agree to come and ride the horse 5 or 6 times and let me teach her how to interact properly with the horse.
It would NOT take a long time to 'fix' this horse. Most horses like this (even ones that are a lot more aggressive than he is) only take one or two good sessions to get them back to being safe and riding & handling as good as they did before they went downhill. Now, that being said, they are not going to be any better trained that they were before they got spoiled. So, if he was not very well-trained (and he may not be if he had inept owners), that is only as nice as he will get without actual training.
Also, I do know most,every horse will test you every day because their mission in life besides eating is to be left alone or be the top horse and with me not being the top horse he will be competing with me.....he is testing me to the point where when I whack him he kicks back even more....
This is the key to all of your problems and needs to be fixed BEFORE you handle this horse or any other horse. Everything you said here is just plain WRONG.
1) If you establish your place as a worthy leader, 90% of horses seldom 'test' you. That other 10% really REALLY want to be dominant and are not testing all of the time.
2) It is not their mission in life to test or argue with people. Their favorite 'safe' place in life is with a herd leader that they trust and feel safe with. It is their mission to have security and to know where they stand at all times. They should never try to be the dominant one in your 'herd of 2'.
.he is testing me to the point where when I whack him he kicks back even more..
No, NO, NO! This is not how you do it. If you are 'whacking' this horse and he is kicking back harder, you are only pecking on him enough to embolden him and are teaching him to be mean. This is how to make a horse dangerous to be around.
If you have to get after a horse more than twice for anything, you did not discipline the horse correctly.
If a horse is constantly 'testing' someone, then the horse has 'a people problem'. The person does not have 'a horse problem'.