I am the father wanting to seek full custody of my 8 year old daugher.

You can modify a divorce decree by showing a substantial change in the circumstances of the parties materially affecting the welfare of the child. The child moving in with her grandmother would be considered a substantial change. You may also modify a divorce decree or a modification of a decree once two years has passed without this showing (substantial change). As the legal father of the child, you will always have the right to seek full or primary custody of your daughter. The legal standard is what is within the child's best interest. There is a presumption in the law that it is within a child's best interest to be with one or both of her parents; not a third party. That presumption may be rebutted in your case because she's been with her grandmother for 6 years. Also, if your child is a bit older (11+), a judge may give your daughter's decision to live with her grandmother or with your considerable weight.

Yes you have the right to seek physical custody of your daughter. There are too many factors to take into consideration regarding your chances of success, but if you do not file, nothing will change. You definitely need the services of an attorney for a case like this. Most if not all family law attorneys will give you a free consultation in the beginning. Call a few, discuss all of the details and interview them, and hire the one you are comfortable with. The lawyers participating in this website cannot solicit business directly from people that ask questions, but you can call the lawyers and should do so.

You have the "right" to "seek" all sorts of stuff. If the Ex has basically abandoned the child with the grandmother, you may have a decent chance at getting what you want.

Yes you could seek custody with those facts. Winning is something else. While parents usually prevail over grandparents, the fact you have waited six years could work against you. Sit down with a lawyer, share all the details and determine your realistic chances.