Major slow down when generating lists and running reports

I'm trying to create a standard list in List Manager (gifts between 7/1/16-6/30/17 that were between $1,000-$5,000) and I have no problem creating the list but when I try to generate it it is taking upwards of 20 minutes to generate the content. The same thing is happening when I try to run a list through a report (like the Fund Activity Report) or when I execute an Output Set. Has anyone had a major slow down like this before? I've run these lists and reports before and they've been instantaneous so I'm not sure what's accounting for the massive slow down.