It sounds like you purchased a U1SG 48" Silent upright piano. This is a very nice Silent Piano. The piano sample in the SG series of Yamaha Silent Pianos (grand and upright) is not the same as the sample in the Mark IV Disklavier. The SG sample is a much newer sample and to me, sounds better than the sample in the Disklavier. I don't know what problems you are having with the sustain pedal of your piano, but your dealer's technician should be able to adjust it to correct any problem it has.
Bill Brandom