When my 700R4 go in to fourth gear and let of the throttle It feel like it in neutral I put it in third gear and it fine The spirometer gear in transmission is to small could that make it shift out of overdrive ?

Transmission was rebuilt

That is because the overrun clutches are on when in third gear, giving you engine braking. They are not on in overdrive. That is why they are called "overrun clutches". When in overdrive (4th gear) they are not applied.