When you forehand attack from the wide forehand or wide backhand, following through back into position should be part of the stroke and technique. Too often players don't so this and so can't cover the other wide angle – and then, instead of realizing the root of the problem, they just say, "I'm too slow!"
If you forehand attack from the wide forehand, you are wide open on the backhand side if you don't get back into position quickly. Use your own momentum from the shot to move back into position quickly. For righties, that means pushing off your right foot.
If you forehand attack from the wide backhand, you are wide open on the forehand side if you don't get back into position quickly. In this case, your natural momentum isn't going back into position - but since you finish with most of your weight on your left foot (for righties), you can smoothly push off and back into position as part of the follow-through.
In both cases, by the time your opponent is hitting his shot you should be in a balanced ready position, ready to cover the table. You don't want to still be moving as he hits the shot - it's better to be slightly out of position but ready to move than moving as he hits his shot, and thereby unable to change directions quickly if needed.
So . . . are you too slow or are you simply using bad footwork technique?