Garage door sometimes doesn't open all the way: belt or opener?
Try disconnecting the door from the opener. Then you can open and close the door by hand to see if there is anything stuck or jammed. Could be that there is a kink in the track or one of the wheels is coming off the rail or something.

If door runs smoothly and without much effort then you can turn your attention to the opener. Note that it may be easier to just replace the whole unit; door openers are not that expensive. I certainly would not call a professional... a new opener is only $150 or so, you could easily blow through that with a diagnostic visit from a tech without actually getting to the real problem.

(If you have never disconnected the door before: there is usually a pull-cord or lever where the curved door arm meets the rail. Pull down to release the door, then push it back up to re-engage when you're done.)