I have a video from the Military channel called "Suicide Missions". It's all about the Shermans in Europe.
Belton Cooper does some talking in it (excellent book BTW) about Hedge-choppers and how he was ordered to equip 50 tanks with them by the next day (after a demonstration by the guy who thought of it).
His entire unit worked all night and completed 7. No two alike. Such are orders.
Anyway...the Pershing was started in 1942, put on hold in 43 (cause the Brass & REAs decided the Sherman could finish the war), so efforts went to improving the Sherman (bigger gun, wet ammo storage, HVSS, etc).
The Brass & REAs then changed their minds after the "Battle of the Bulge", and the Pershing was completed (with underpowered Sherman engine), and saw limited service.
Cooper speaks of recovering a few knocked out ones in his book.
If...they would have kept after the project from the start...from D-Day onward, U.S. Armored Divisions would have had 1/3 Pershings, 1/3 Shermans, and 1/3 M-5s.
Perhaps Panthers & Tigers wouldn't have run "Rough-Shod" over Alied tanks, and more young men would be alive today.
Such is the danger of REAs who have the Brass's ear.

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"Danger Will Robinson!"