hi there
HVSS is Horizontal Volute Spring Suspension. it is the later suspension which let the tank travel better over rough terrain.
Also the Sherman T-23 was
The T-23 turret with the M1A1 L/53 76mm gun was originally designed for an experimental American medium tank design also known by the same designation "T-23".
there is a little more information at
more info here and some more here
more info