The 90mm short barrel could barely eat a Panther and it was a bit "iffy" against a Tiger/King Tiger so the US Army messed with the longer 90mm anti-aircraft gun. They then welded armor from captured/knocked out Panthers to the front of the Pershing. At long range the long barrel 90mm AA round could eat a King Tiger for lunch and spit the bones out. Likewise, it could hole the Jagdtiger at medium range.
The war ended before the Army needed more than a dozen. The Marines remembered the mod and when faced with T-10's, they quickly modded their Pershings. As the longer gun fired hotter rounds, the rounds were bigger and they carried fewer. So since fewer rounds were left for ground support, they jury rigged the rocket launchers.
Marines at Chosin used the "rocket generals" to blast their way out of the T-10's that the Chinese/NK's had surrounding the area. So that's gonna be my next Pershing. But much later. Maybe next year or so. I'm armored out at the moment...