The Light Blues looked like they would hold on for a 2-1 win in their quarter-final tie against Queen of the South at Ibrox in September 2012, until Gavin Reilly forced the game into extra-time with a last-gasp equaliser which the home side vehemently claimed was offside.
The tie was still deadlocked at 2-2 after 30 added minutes and it was the Dumfries side who came out on top in the penalty shoot-out, which still irks the Gers boss.
"We are treating it as a major cup final," said McCoist. "We got enough stick last year when we didn't get in it.
"Actually we are still a bit sore from last year, a controversial goal took it to extra-time and we lost on penalties.
"I've always said that we want to win every tournament that we enter at the club and the Ramsdens final is no different.
"The lads have done well to get to the final, as have the Rovers players, and both clubs are taking it very seriously."
McCoist is aware that for many people, a more important game for the League One champions is the William Hill Scottish Cup semi-final against Dundee United at Ibrox the following week.
However, the former Gers striker, with the knowledge that his side are odds-on favourites to win the Ramsdens Cup final with all the pressure that brings, will not allow his attention to be diverted from Leith until Sunday night.
"I don't think we are in a position to look ahead to the following week because the next game, being a cup final, is the most important," he said.
"We will prepare for the Dundee United game after the Ramsdens final.
"A lot of people will see us as favourites in the final which is fine.
"Many would expect us to win the vast majority, if not all the games that we play, so that leaves us open to a little bit of criticism if we don't.
"At the same time it is a completely different situation, one that we haven't been in before. We are in the league below the team we are playing.
"It is a cup final involving a Rangers team which is completely different to previous Rangers teams who have been in cup finals.
"We have never won the tournament before and you want to win every tournament you enter.
"I've always said the most important thing is to get out the league that we are in, but we have an opportunity to win a cup on Sunday and we are not treating that lightly."