A G5RV has a very high SWR on 15m. My first guess is that the impedance is just out
of the matching range of the tuner.
How low can you get the SWR on 15m?
What are the capacitor settings at that point?
It may be that adding an extra 6' to 12' of coax between the antenna and the tuner
will change the impedance to where the tuner will match it.
It is also possible that there is some sort of internal problem - for example, if the
roller inductor is dirty in the part of the coil where one would normally tune for 15m
(possibly from using it at high power into a G5RV) or the "Self-Resonance Killer" circuit
might not be switching properly. But I'd try the extra length of coax first and see if
that makes a difference.
Lowest SWR reading is 1.8 to 1 set on Letter E....& it goes higher the higher I go up in the phone spectrum, with the power output decreasing.......No other settings budge the swr in any way....I don't have this issue on the smaller tuner....flat match all the way......I will take heed of your advise and see if I can clean the points and extend the coax....