The Futon Critic reports that Saving Grace will return for its final season of 9 episodes on Monday March 29 when TNT will air back-to-back new episodes from 9pm-11pm. The following week it will take the Monday 10pm slot.
Previously, TNT had announced Saving Grace would return this summer. It seems likely it will still finish in the summer though. It will only get four Monday airings in the spring (including the two episodes on March 29) before the NBA playoffs on TNT get in the way on April 19.
Separately, Southland will finish up on Tuesday, April 6 at 10pm. Leading into the finale, TNT will be airing a marathon of the five episodes of season two that will have already aired by then.