As many have said changing the tuning keys can make a difference IF that is the problem. I would rule out everything else first. Things like neck alignment, fret wear, nut, bridge and tailpiece. If they are ok then check to see if your tuning keys can be tightened. Sometimes the nut and/or the wood screws that hold them in place can come loose. If you are not sure how to do this then take the guitar(s) to a tech.

Then if everything is ok unstring the guitar and see how easily the tuning keys can be turned. If they turn very easily then that is your problem.

Ps – if your strings are old then you can never keep them in tune regardless of what you do. Also on very rare occasions you can get a bad set of strings. This has happened to me once, a brand new set that I could not keep in tune. That taught me too never by bargain strings again!

I want my last spoken words to be "I hid a million dollars under the........................"

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware