Have you tried the no cable needle method of cabling?? Here is a link you may find helpful: http://wendyknits.net/knit/cablelesson.htm
. I, too, always had problems with loose stitches when doing cables. I found that because I was pulling and tugging on the stitches and trying to manipulate the cable needle all at the same time, that the stitches became distorted and loose, like you say. When I tried the method linked above, the problem went away. You might like to give it a try.