At about 30mph cruising on flat ground my 700R4 jumps back and forth between 2nd and 3rd gear. It's not in OD. The only way to get rid of it is to either speed up so I'm constantly on the pedal or to take my foot off, coast, then speed up again... Anyone know what's causing this? The previous owner said the tranny was rebuilt recently less than 10K ago... I know, I know, he could of just said that. Either way, anything recommendations??