Maybe a nerf to PIV reload speed could fix that. Its a very good (some say best) medium tank, should not win against USF only high end tank destroyer imo.
That is a horrible idea nerfing reload or even nerfing PanzerIV. It costs a lot for a medium, costs the same/similarly as Jackson but both have different purposes.
Jackson, has better mobility, range, penetration. Has even a crew that can heal their own tank. Better accuracy on the move. AT purposes. So it is superior in AT terms a specialist.
PanzerIV, slightly more armour than regular PanzerIV, can go against Infantry, is also mobile. Is a generalist.
If you know how to kite, then you would come up with better ideas than nerfing reload of a tank that does the same damage as any other but with less accuracy.
Jackson is at a good spot.
If you do not support the vehicle and make it vulnerable to flanks. Than that is your mistake. Jacksons can even flank PanzerIV too, it is vice versa.
The issue is heavy tanks really. That changes the whole balance situation.