How can I make steak and chicken on a gas grill that's tender not chewy?

I'd suggest your guy cook his own damn steaks. You can improve flavor and to some degree tenderness by buying top choice or prime beef, and by dry-aging/marinating the beef in the fridge before cooking. When I buy good beef, I take off the wrapper, sprinkle it with Montreal Steak seasoning, and let it age in the fridge for four days. It will darken and dry on the surface, but you are developing flavors in the meat. Cook at 400° F on the grill with the lid open. Turn them at the four-minute mark. Use an instant-read thermometer and cook the center of the thick-cut steak to 131°, medium-rare.

I have never heard of a gas grill that's tender. Usually they're made out of steel. 

I am sorry, you may think I am ignorant  but you cant 'make' meat, you can however, cook it. Is that what you mean? and what is a Kabob or is that a typing error?or do you kebab?

my advice is to have the whiners cook their own dang meat.  How dare they complain!?  You should have more respect for yourself than to take that kind of carp from them!

Buy quality beef and you shouldn't have any issues.  Cook on high heat; let it rest 5-10 minutes before cutting and slice against the grain.

Google for help on this [It may just be a case of marinating the meat, or the correct heat setting?]

How many old accounts do you have that you can jump on to continuously ask the same questions? It's mind blowing really.

Buy higher quality meat. Cook over high heat for only a few minutes on each side for medium rare. Don't over cook, warm red center would be good, pink is fine - but better meat is often the solution.