I have played for 41 years and I have found the best tuning is accomplished with an electronic tuner. The grade of instrument, no matter the brand has a lot to do with it also. Your instrument may have a warped next and you may be able to have the warp adjusted out. To see if it is warped, look down the neck from body to head stock. There may be slight twist. You also may have a box in your neck. Place a metal straight edge on the full length of the neck and hold it eye level. This can also hopefully adjusted out. When all else fails, take your instrument to someone who knows how to work on your type of instrument. Good craftsmen are hard to find. Don't trust any TOM, DICK OR HARRY to work on your instrument. I play a l967 Martin D-28 and like my instrument very much. It tunes easy and holds its tuning for quite a long time. Wish you the best. It happens to the best or better of us. Part of playing, I guess.