Lee was respected on both sides but with the Civil War still just about in living memory, I would have thought Sherman a more divisive namesake. Did any southerners raise objections to naming the Sherman after the general who had laid such waste to the region?
In fact, there were no complaints because the US Army didn't actually name either tank, the British did.
Officially the US Army listed the Lee/Grant as "Medium Tank, M3", while the Sherman was the "Medium Tank, M4."
The Brits, who actually gave names to their tools of war (see "Hurricane," "Spitfire", "Gladiator," "Brisfit," "Camel," "Bobolink", "Walrus", etc), realized that it was quite easy to confuse the M3 with the M3 light tank, and thus the "Lee" moniker was born.
It wasn't until after the war that the US Army started to name tanks after generals without help from the British.
The same often applied to US aircraft used by the British. They were the ones to name the P-51 the Mustang, the P-40 the Tomahawk/Kittyhawk, the PBY the Catalina, and so on.
It should be noted that this does usually NOT apply to US Navy, who did name their aircraft. Attempts by the Brits to apply their own names to US Navy planes (the F4F Martlet, for example) generally went by the wayside quickly enough.