I also have a grace frame where the plastic tracks are not smooth. This probably would not account for the skipped stitches, but it makes the machine difficult to move as the carriage gets stuck in the damaged areas. Could you elaborate on what you've tried so far so we can try and give you some ideas rather than repeating what you've tried?
Often fraying and skipping are needle issues. Try a larger needle. make sure it is inserted the right way and all the way up the shaft. I'm thinking you have a 'next generation' frame. Make sure that the take up roller is adjusted correctly. It is very tempting to raise it up so high that you don't have to do it as often, but if it's too high, you will get skipped stitches. You should just be able to get your fingertips between the quilt roll and your machine bed.