Mike hit the nail on the head. If you have the ECM turned up you will drive thru the trans. You may or may not know when its happening but believe me, it's happening. If you notice the trans "hunting" meaning going in and out o/d you should shut it off. The other thing that happens when they shift back to 3rd gear is the T/C unlocks and locks. This is a wasted move you can only correct with a T/C lock overide switch. For years it has been said that overdrive is not as strong as direct. I just built my first 4R100 and I can tell you the planetary in overdrive is the same size as 1st.