[78P930]

I recently replaced the synchros on my 930 transmission, did not mess with the shift forks and now it won't stay in first or second gear. Any ideas on what I did wrong before I yank it out again? I rebuilt the transmission b/c it would grind all the time going to second gear and also I couldn't get it in reverse after having to force it into 1st at a traffic light(still a problem). Any help appreciated.
Pat