You need to let your birds refrigerate for a few days to age. Until the meat has a chance to go through rigor it will pull up when heat is applied. Personally I soak the first 24 hours in fresh water. Dump water and then put in a brine and soak for at a couple more days. It is best to submerge the birds completely that way the birds are cut off from any air to help bacteria develop. A solid bird should sink to the bottom, and when soaked in brine and it surfaces it is ready to cook. Also check for stiffness, if the joints are still stiff it is not ready yet. If you cut your chicken up leave the legs and thighs as quarters so you can check the joints. Then seperate when ready.
Some restaurants use the large commercial Rubbermaid garbage cans to soak their birds in a walk in cooler. I put mine in a 3 gallon bucket on the bottom shelf of the fridge. Check the brine for any sign of smell during this process, I have never had any but always be safe. This is the way we always did wild game before cooking and it was always tender. You can also substitute tomato juice for the brine. We used to do a milk soak on boneless chicken breasts the night before when cutting into strips for fried chicken strips. Milk soak also works great on beef cutlets for country fried steak.