Can you post a photo here? OR at the Plumbing Forum? For starters, turn off the water supply, then unscrew the handles. Probably worn out old washers in there. You can take one of those old washers to the hardware store and get some that are the same size. -Babka

First thing I'd do is read the installation instructions to see what is specified there. If they recommend "X" number if vertical inches and you're less than that, or if you used PEX and they specify "no pex" or you used pex that has a smaller inside diameter than the recommended tubing, then essentially you have an installation issue. 1/2" pex does have a smaller inside diameter than 1/2" copper. For delivering water volume to a faucet it's normally not a problem, but when depending on a specified vertical water column, I guess the smaller diameter of the pex could be an issue. I'd call the manufacturer's tech support line and ask them about remediation. No harm no foul, it's best to run ideas past them before you crack open walls. You installed the shower head lower for the kids. Let's say you have yours 25" above the valve and the manufacturer specifies 30". What you could do is have the pipe come vertically out of the valve, and run it up the wall several inches higher than the shower head, say to 40", or even all the way to the top plate of the wall, then add a couple of 90's (to create and inverted "U") and then run it back down to the shower head. That would take care of the vertical issue while allowing you to still have a lowered shower head. If your pex to the tub spout is constricting flow out of the tub spout, that might need to be changed to a larger size of PEX or to copper. Something with a larger inside diameter. You're on your own well so it's likely excessive water pressure isn't an issue. What's on the "back" side of the wall that the valve and plumbing is installed in? Often times it's easier to cut through the back of the wall to access the plumbing, repair the plumbing, then TEST the plumbing, then patch the hole, than it is to access through the shower side of the wall.

@sven_erte - you are thinking about replacing - there is another option - u could simply replace the handles - since u have identified the manufacturer u can review their online catalog and get that done. With regards to the spout - u might consider re-plating the spout to give it a newer look and replacing the aerator. this way u can still be assured that you are getting a new look but not taking on any risk by getting a new spout. There are some highly rated faucet plating companies which you could use.

Call customer support at American Standard and see if the hose part number below can be spliced so you have the length you need. Part number-051343-0070A 1-800-442-1902 Monday through Friday 8:00 A.M. to 6:00 P.M. EST Technical Customer Service Monday through Friday 8:00 A.M. to 6:00 P.M. EST 8:00 A.M. to 3:00 P.M. EST Saturday