Above 21MHz I have a very difficult time tuning the antenna to get any SWR
below 3:1.

Hi Larry, My good friend Reg Edwards pointed out some time ago that most
antenna tuners give it up above 21 MHZ. This is due to stray Inductance and
Capacitance in the Garden Variety Antenna Tuner. Makes it real difficult to
tune certain antennas above 21 MHZ. As others have mentioned, change antenna
length, or feed length and see what that does. There are programs that will
determine correct tuner settings for a given impedance, I prefer the Smith
Chart.
If you can determine the Impedance, R+/-jx of the feed point, there are a
number of alternative ways of designing a matching network.
73 Gary N4AST