The Glasgow side crashed 3-0 at fellow-playoff hopefuls Queen of the South on Thursday to end manager Stuart McCall’s six-game unbeaten run.
McCall led the side to three draws and three wins before James Fowler’s men brought them crashing down to earth with a comfortable victory at Palmerston Park.
Rangers now find themselves in third place – behind champions Hearts and Hibs – and could be forced to play an extra two matches if they fail to secure second spot in the table.
The fourth side in the Championship – likely to be either Queen of the South or Falkirk – play the team in third over two legs for the right to face the runners-up, with the winners taking on the team who finish 11th in the Premiership for the right to play top-flight football next campaign.
Rangers, who inflicted only the second defeat of the season on Hearts last weekend, looked favourites for the second spot before coming unstuck against the Doonhamers and it is that in-and-out form which Miller believes could cost them games against the likes of Celtic, Aberdeen and Dundee United next season.
“Last night was a reminder that we have not turned the corner and that there’s a lot of hard work still to be done,” said the former Celtic and Scotland striker.
“It was a performance that summed up our season a little bit. That ‘consistency’ word has come up a lot this year. We seem to have a couple of good performances and then complacency kicks in and we take our foot of the gas.
“If we go back three games to the Hibs result, I don’t think anyone could have seen that coming. Fast forward three games and I don’t think anyone could have seen the result last night coming.
“We have to nail down that consistency and get to a level of performance that we can pretty much guarantee every week. Might this inconsistency come back to haunt us in the play-offs? It could do,yes.
“There is no point winning 1-0 or 2-0 at home and losing 3-0 away – that means you are out. It’s about getting that level and balance right. We need to get back to where we were at against Hibs and in the first half against Hearts, where I thought we were superb.”