Whitey

I need a drill that can handle a 6" hole saw. I work for a mechanical contractor and have to drill holes in metal roof decking. It's not often I need to drill a 6" hole but on occasion I must. I have a small Makita corded sds rotary hammer I've used for years in residential work, but it just isn't enough for the work I do now. It keeps clutching out on me just cutting through the foam of the roof deck before I even get to the metal. I admit that the drill is close to 10 years old and used hard, so I'm sure it's raged out witch doesn't help.any suggestions?