I've only had my 99 for about 3 months now and its all been fine up until a couple days ago. I have a triple disc converter and a aftermarket valve body mind you, but when I hit 45 and overdrive is on, it will shift and lock then unlock and do this about 3 times or until I get over 50mph. It started doing this with overdrive off also and when I hit 25-30 it will do it also. What is the problem?