"Is the Great Pyramid the first pyramid with a granite chamber? " depends how you classify a chamber, the granite construction at the bottom of Djoser's pyramid perhaps?
The sarcophagus in mastaba 17, would appear to be contemporary to the pyramid next to it. Petrie states that the body of the mastaba was made from clean limestone chips, from the waste of the pyramid. Wainwright also thought that the mastaba filling was contemporary to the pyramid. The Meidum complex appears not to have been finished; the temple was not finished, and even the stone facade discovered by Maspero, on the east side of the mastaba was plain, and uninscribed. Given that there is no entry to the substructure in mastaba 17 from the surface, and that this huge mastaba was carefully constructed on top of the already inserted sarcophagus, it would appear that the sarcophagus predates the mastaba. This mastaba was a careful construction, and Wainwright discounted that it was built after the finishing of the pyramid.