Keep in mind that the pershing also has the very strong combined arms ability, which gives the tank EXTRA range essentially giving it 60 range and 60 sight range, and its special ability is not an AP shell, but a piercing shot that pierces buildings. Like ISU-152 piercing shot.
Jacksons with more than 60 + range + self sight , ouch. The commander is going to have alot of lategame power.
Overall i can't believe some people think the pershing will be bad. The pershing is suprisingly perfectly balanced and its stats are just right. They fit in the american design of fragile, mobile and hard hitting very well.
That's more an issue with the combined arms ability. Unless it's a passive ability (which would be OP) i don't think it should be balance around it. Knowing this, i don't think messing with range is a good idea. Sight and RoF, sure.
This design of the units is fine if you combine it with this and that doesn't work. See Valentine and Sexton, post nerf Osstruppen and Artillery officer, FHQ and 45mm AT gun, etc.