Step Aerobics

Hi all! Finally reached my goal of 47lbs. It's actually 51 now! I run 3 days a week about 5-8 miles per session. The other 3 days I do DVDs with weights and resistance bands. My running times have improved significantly but on my long runs I find my knees getting really sore. I used to do step aerobics years ago and have a couple of Kathy Smith VHS tapes!!!! But want to get something new. I still have my great old step but I was hoping for some great new recommendations. Thanks!!!