904 with Turbo Action shift kit, no 3rd

I would pull the valvebody off and check the 2-3 shift valve.The 1-2 and 2-3 shift valve are next to each other in the valvebody.
Take an blow gun and put your thumb over long slot next to the steel plate farthest from the pressure regulator and with the blow gun shoot some air into the passage with your thumb blocking the rest of the port.
You should see both valves move back and fourth with the air pressure.
When you have taken the v.b off,did you take it apart?putting a valve in backwards or leaving screws loose or over tighting screws will also cause problems.
If this was a working unit before your rebuild,you should be able to find the problem.Shift kits just add to the fun.
Also air check your your clutch drums through the case in the front,if you have a cut seal it may be possible have reverse because of a higher working line pressure in reverse.
When you reassemble the t.v lever make sure your e clip is on the shaft.I have seen people ram the lever on and the lever inside will get jammed in between the pressure adjustment and the bracket causing no rise in line pressure.
If it is all to still in the car do a line pressure test to check your pump pressure.
Good luck keep at it you will find your problem:D