727 Installed - No Movement in Gears

I have had a similar problem with my 727! No reverse. After pulling the box back out and replacing every seal we could find and putting the box back in , still no reverse. Wr dropped the sumMine is a 1978 727 transmission.p and put a standard valve body in and presto reverse now works. The shift piston in the valve body with the transgo kit is completely different than the standard one so down the track we will put the old shift piston in and try that valve body again. Have any of you guys had this issue with trango kits? Mine is a 1978 727 transmission in a small block.