hiccups at high speed

I just took my 01 Panther out on the open road and got it at the top of 5th and it started hiccuping at about 70-75, and continued as long as I was up there, about every 3-4 seconds, like a hesitation. It almost sounded like it was misfiring... does anyone know what this might be? I went through a few tanks of gas, so it wasn't bad gas. I have a Vampire exhaust and Twinair filter, but otherwise stock. Anybody else have these issues, or any ideas? 
