Is an appellate court's reversal of a trial court's grant of a new trial reviewable?

QUESTIONS PRESENTED 1. Ia it reversible error when an appellate court overturns a trial court’s grant of a new trial when, first, the decision to grant or deny a motion for new trial is not reviewable; and second, the trial court’s grant concerns factual sufficiency, . . which is not to be confused with legal sufficiency and the due process standard of Jackson v. Virginia, 443 U.S. 307, 99 S.Ct. 2781, 61 L-Ed.2d 560 (1979)? 2. Does the law-of-the-case doctrine prevent a high court from considering the correctness of an appellate courts decision? ; ii