To modify this system to run at higher speeds - using a sliding block system, for instance, means making the system incapable of firing standard 155mm ammunition. There have been 155mm SP guns that have been automated to load and fire ammunition faster but they have required a heavier loading system to do it - like the French GCT gun system or the PzH 2000 or the US Army's Crusader - which makes the turret very large and heavy.
To make something large and heavy move faster requires very large actuation systems which in turn, require much greater power.
Very quickly you begin to see a 70 ton gun system which can't cross bridges and is very hard to transport by air or sea to the forward combat zones. It's all possible - but the penalties are weight, expense and an entirely new ammunition system.
Don't even consider the towed 155mm systems - dang things are heavy, manually operated, and slow; my best gun crews were flailing for 12 minutes to emplace and ready their guns to fire when they rolled into a new position. And that was with ten strong young men doing their level best!
However you did address my question as positioning. You said: "To make something large and heavy move faster requires very large actuation systems which in turn, require much greater power."
I would agree with your above analysis regarding actuation and needed power. Basic physics.
Still, I ask can't nuke powered ships re-direct their power to the gun, especially Carriers or CGN's? As a sailor at general quarters I knew that many systems were shut down to give more power to defense and offense and damage control. That was way back in the Cold War, so I don't know how the current systems work, especially on nuke powered vessels.
My point still remains, if these Mark 5 kinetic rounds can be operational, why can't we make make the Howitzer (or a new cannon) more ready capable with radar instead of some old battleship gun pointing in the general direction? I'm thinking I may off base, again no knowledge of artillery.