If you've already checked the neck relief, you can check for a high fret by using a straight edge. Grab a credit card or something, centre it on a fret and then see how much it can rock backwards and forwards against the adjacent frets. If the frets are level it shouldn't rock, especially if you have some neck relief. You can buy luthier "fret rockers" for the purpose, but a credit card should give you enough of an indication - better still if you have an old one you can cut up as ideally it should cover just 3 frets
Edit: Use the edge of the credit card to check (just to be obvious )