Dripping shower head

Obviously this is a leak in the valve. They are no fun to work on. Some of the higher end models of valve have seats that you can change and along with the ball and other hardware, that should stop the leak. If not you will have to replace the whole valve assembly.

follow this steps and fix it. God bless you
If a faucet leaks, replace seals and gaskets .
If a shower head leaks, create a better seal or replace seals .
If a sillcock wears out, replace the washers .
If a compression faucet drips from the spout, replace the washer and/or the seat .
If a faucet leaks from the handle, replace O-ring(s), replace the packing washer, tighten the packing nut, or replace worn packing, depending on the valve type .
If a ball or cartridge faucet leaks from the collar, replace worn O-rings .
If a disk faucet leaks around the base or has reduced flow, replace cracked or pitted disk assembly or worn inlet seals .
If there is water under the sink, tighten the faucet-set locknuts under the sink. You also can replace putty or a gasket, replace a worn faucet, or replace leaky supply tubes .
If the aerator leaks around the edge, replace the washer in the aerator .
If the spray hose leaks or has reduced flow, replace the O-ring on the diverter valve, replace a worn washer at the base of the spray head, or clean the diverter valve and spray head .

You could have a restriction in the tub spout or just too much pressure. Diverter only restricts flow to tub spout so any restrictions to the tub spout will cause water to go up to shower head.

Yes, and I do recommend that you do not use danco cartridge's unless you can not find any other brand. Kohler would be best if they are still available.
This link will help with ordering parts.

http://www.kohlerserviceparts.kohler.com/Product.aspx?modelid=3036b09acd6f4870a974f463706786e8&returnurl=http%3a%2f%2fwww.us.kohler.com%2f%2fonlinecatalog%2fdetail.jsp%3fitem%3d524302%26section%3d2%26category%3d8%26subcategory%3d50%26retail%3dfalse

there could be dirt in the shower head or the two way divertor valve. i would remove the shower head first.

You need to order seals and replace them. Typically, dirt in the water system damages the rubber (neoprene, plastic) soft parts. Sometimes the damage wrecks metal parts, but this is less common.

Did you use plastic pipe? What about the shower head? Does it have a rubber o-ring in it? Pull the pipe out of the wall at the shower head and peek inside for the o-ring. If it is there, just snug up the pipe, do not over tighten. We were ready with crow bars in hand to destroy a brand new shower we just finished, because we thought we had w broken pipe, Then the owner says he torqued up the shower head as tight as he could and I read where it had to be just finger tight. One more place to check is the faucet itself, take off the trim ring and look in there for drips. It could be filling up the wall cavity and stay wet for days. I would take apart the drywall on the other side before busting up the tile again. Check it out.

If the problem is solely because of the rubber washer with screen you can buy any cheap replica hose and use the washer that comes with it. If the issue goes away you are done. If not, switch heads and see if the issue follows the head. If it does then there would be a crack in the head at the connection. If neither solves the issue then you must buy a new hose.

Remove the screw and screen, then the 2 allen wrench screws and check the spring and valve in there, they might be sitting incorectly, adjust and re-assemble. Check pic for help.