Most of the ELPAC I measure come in at 5.2 volts. The 5.4 should not be a problem. There are many voltage regulators inside the Touch to change the nominal 5 volts into the various voltages the the many chips need to work.
Did you measure the voltage no load? The actual voltage when plugged into the Touch may be a bit lower.
If it doesn't vary much, then this is a very good candidate for installing a Bybee Music Rail
At this age, there is really nothing you can do about the hum. More than likely the laminations and windings are started to part. The epoxy can only hold together for so long.
