Well, there was a replacement for the M551- it was called the XM-8 Buford and was cancelled in 1996. It had a 105mm rifle mounted with an autoloader so the crew was three. I did hear that thanks to Iraq the 82nd is re-evaluating them for use, or at least looking at them, but that was from Wikipedia and also from 2004.
The Sheridan was a maintenance nightmare and even the NTC got rid of them. The whole gun/missile system was also tried on the M-60A2 tank, which also bit the dust due to issues. It had one huge honkin' cupola on it and a very bizarre turret shape that looked like a retangular box on a bagel.
There are a lot of failed US tanks out there. Do a search for the M-103 to see one very large tank.