My SWR's are basically flat on the lower end of the 2m scale, but there is a
significant jump starting at 146.000 thru 147.999. Starting at 147.000,
it's pushing the 3:1 threshold and going over the 3:1 threshold the higher
in the freq band I go.

I have a discone antenna and would like some suggestions as to tuning
methods. From what I know, if the SWR's are high on the 'top' end of the
range, the main vertical whip needs to be trimmed.

Does that sound right or is there something else I need to check on first?

Thanks.