That transmission will free wheel when the overdrive is engaged if you let up off the gas. There are two areas that must be filled with oil. The overdrive fill plug is to the rear . Make sure that the speedometer gear is seated inside the transmission fully then tighten the cable. If the oil level is low like any transmission it will not shift properly. I took my overdrive out and put my regular transmission back in because I did not like the freewheeling with the drum brakes on the freeway. Gook luck with thr repair.