weird problem

Just swapped a 65 dart four speed into a 64 Valiant. 225 slant motors in both. The first time I shift from first to second - its like the shifter is hitting a brick wall - won't go into second at all. I can shift to third and its fine. Once the gears have been gone through once, I can shift into second without any problem. Any ideas on what is causing the problem in second gear on the first go round? Has me and my mechanic baffled. Dave