Your RadGrid definition seems OK. Setting SaveScrollPosition="true" successfully saves the grid scroll position on AJAX and you get the position persisted on AJAX requests. Attaching a test page to demonstrate.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items