I also use a slice of bread to keep them soft longer in the cookie jar. I agree with butterflyblue--check your oven temp and do not overbake.
I have a cookbook titled "Chewy Cookies" by Eileen Talanian. It explains that the ratio of ingredients and the timing are the keys to the texture. (I've used several recipes from the book and all have been good.) Of course, chewy and soft aren't exactly the same thing, but maybe learning the science behind the baking will help you determine a solution. Keep on trying!