HRBE wrote:
Why are the 20m whips the only ones giving me trouble?

Probably what is happening is that you are getting a
self-resonance on 14.2 MHz from the 75m or 40m hamsticks.
That doesn't happen with 1/2WL fan dipoles but it certainly
can happen with hamsticks. For instance, if the self-resonant
feedpoint impedance of the 75m hamstick dipole is lower on
20m than the 20m hamstick dipole, you will not be able to
adjust the 20m hamstick dipole for a 1:1 SWR.

Using only the 75m hamstick dipole, find the 20m impedance.
Then do the same for only the the 40m dipole. You can
probably diagnose the problem but I don't know of a
solution.
--
73, Cecil http://www.w5dxp.com