Mustang throttle sticking

I have a 1998 3.8 v-6 auto with 79k. It sometimes acts like the throttle is sticking. If I accelerate to say 35 mph and take my foot off the gas as long as I'm on flat ground the car will continue to go that speed until I hit the brakes or a hill. It seems to do it primarily around 30-45mph. I have cleaned the throttle body, maf, and iac. That's not to say they can't be bad but where should I start?

Thanks,
Derek