Rangers came from behind to beat Morton and extend their lead at the top of the Championship to 15 points.
Denny Johnstone gave the visitors a surprise lead midway through the first-half after an error from Rangers keeper Wes Foderingham.
Miller headed them level a minute before the break before grabbing another two minutes after the restart.
Lee Wallace added a third as Rangers extended their unbeaten run to 15 matches.
With Hibernian absent from Championship action this weekend due to Sunday’s League Cup final with Ross County, the Light Blues’ nearest challengers remain second-placed Falkirk.
Four more wins from their eight remaining matches will seal Rangers’ promotion back to the Premiership.