7004r won't shift into 4th

[jfoley]

1972 blazer 4x4. Since I have had my blazer the 700r4 won't shift into 4th. When I bought the truck before I drove it I swapped in a tilt column from 1971 blazer I had so I don't know where the problem lies... Park, neutral and reverse all match the indicators on the column. I thought maybe the selector was off but if I try to move it from "D" in the direction of "P" it just pops into neutral. I can't find anywhere that shows where the selector on the transmission should be for "OD". I adjusted the TV cable yesterday, shifts into 2nd at 10 mph, 3rd at 25 mph. TV cable is pretty hard to pull. Seems to shift fine, It wouldn't kick down before I adjusted the cable, and I haven't tried to see if it would now. Also the electrical connection on the drivers side is blocked off

Thanks for the help