zafira hard to get gears ?

hi can anybody help i recently changed engines from my opel zafira 1.6 16v v reg i did not change the clutch plate i took of the clutch checked it it looked ok then put back together i then put the engine in i left the gearbox in when i replaced the engine it all bolted bk together ok. now its hard to get into gears when the cars driving when the car is parked and not driving the gears go into gear ok its just when the car is driving i can get all the gears but they are stiff could i ov bent the gear linkage or if the linkage has bent i would of thought it would be hard to get gears at all times gearbox oil is full any ideas of what it could be