[Elecraft] KX3 10W not 15W?

[Ken]

Hi all,
I've had this used KX3 for a little over a year now.
I've always set the PO to 15W's. Decided  to check the PO with two meters a while back and the max it puts out is 10W's or so on any band.
I put the latest firmware in it a while back and it's still current.
Power supply is the Pro Audio Engineering. 14.1V at 4 amps or so but it does the same on any PS.
Certainly 10 watts to 15 will make absolutely no difference whatsoever at the other end, but it just indicates somethings not well!!
Any info appreciated.
Thanks!! Ken, W2GIW