I think you might be mixing up some other paramilitary organisations that exist in Ireland, most of whom have added to that figure.
Over 3,650 people have been killed as a result of the (stupidly named) 'troubles'. But of that figure, many were not as a result of IRA action. You have to factor in numerous other groups, splinter groups, plus the British Army (who've shot quite a few people themselves). Just off the top of my head you have the Ulster Volunteer Force, Loyalist Volunteer Force, Ulster Defence Association, Ulster Freedom Fighters, Red Hand Defenders, Red Hand Commandos, The Orange Volunteers, The Irish National Liberation Army, The Provisional IRA, The Continuity Irish Republican Army, The Real IRA. And probably The I Can't Believe It's Not The Real IRA and the People's Front of Judea too.
The IRA have indeed killed a lot of people, but to suggest that only the IRA are responsible for the death toll in the troubles is misleading.
The troubles in Ireland are not a simple affair. Much of it, for example, has absolutely nothing whatsoever to do with the religion and the nationalist desires it often hides under, and is more about a drug-dealing turf war in many areas.

Chock