You might want to try this! Next time you go out and you are working on your 2-handed backhand, try to keep both of your arms straight as you prepare to run for the ball. Let the racket that is in front of you take you to the ball. You can run much faster when your arms are in front of you than when you are dragging them behind you. If you are right handed for example, run to the ball and stop on your left foot. Then, let the right foot step out, taking your racket and shoulders back as a unit. This concept will help get rid of many of the errors you have been making using too much wrist and your elbows being bent too much. Your backhand will start feeling tighter or you will find that there are fewer things that will go wrong. Each pro might tell you something a little different on how to change your grip, but this concept will still make you better.
 
Also, keeping the arms straight will definitely shorten your backswing and help you handle faster balls, especially when you are scrambling.
 
Good luck on the courts!
 
P.S. I have a class of four women, the youngest is 72 and oldest 83 years old. They are fit, have long rallies, cover all the balls hit to them in a large 3-step radius. They are still learning, having fun, laughing and giggling, and then they go out to lunch after the lesson. They all have problems, but you never hear about them. What a joy! -- Get off your butt and get on the court and play tennis like these ladies!!