Vibrations thru gas pedal at bout 70mph

While drivin on the highway my car starts to vibrate almost to the sense of a heartbeat , off n on every other second! I'll feel a lil rumble, then stop thru the gas pedal but crazily if I go bout 77 it will start to fade!!! I usually just stay at 67 so I can barely feel it n not get a speeding ticket either lol! Any help, I was thinkin wheel balance but I've had one within the last 3 mos! I thought I only need a wh balance if I get a tire on the rim , not just takin the wheel off to do the brakes or anything which is the only time I've taken it off! Thx for the help!