You are seeing the results of using the ATU for
a purpose it was not designed for. Internal ATU's
in general, were never intended to be used as full
range tuners. They were intended to be used as
"line flatteners", where the mismatch is not too far
out of line...I would use a stouter outboard tuner to
do what you are doing...It's doesn't have to be fancy.
A simple L tuner would probably match most of what
you are doing...BTW...On the bands with very high
SWR, your loss using that rg-58 is going to be
substantial. How bad, depends on the SWR. If you
are under 5:1 or so, not too awful bad...Over 10:1,
it's starting to be loss oclock.. MK