idk man i mine does something like that every now and then. ill be in between 55 to 70 like you said. i would hit it two and let off bc i dont want it to drop into second i just want it to stay in third. so it drops into second for about a second and then i ease off a little and it shifts into third but dosent accelerate for about three seconds, like its just slipping. i know its not just me bc my buddy felt it too once.