After my engine rebuild it seems as though the transmission is having a hard time shifting. When I'm at idle, I can go through all the gears easily, but when i'm actually moving it's very hard. If I don't pull it out of gear at the exact moment I hit the clutch then it won't get out of gear and I have to yank it out of gear. When I try to shift into the next gear, it won't go in at first - I have to keep putting pressure on the shifter until it finally pops in. When I try to downshift, it won't go into gear unless I rev up the engine to match the rpm's. I don't think it's the shifter cables because I can shift through all the gears easily if I'm not moving, it only gets hard when I'm driving. Any ideas on what could be wrong? I was thinking maybe the synchros but this happens for every gear, not just one or two.