If the transmission input shaft is spinning at a different speed then the wheels + gearing it's extremely hard to move the shifter into gear. If you force it, it'll go but it requires like punching the damn thing in and it doesn't grind its just extremely difficult to move. Its most annoying when I take it out of gear when slowing down for a stoplight and try and put it in first as I slow, but it also happens with any other gear. basically, in order to get it in, I have to double-clutch it or get the revs really close between gears. The transmission fluid was replaced less than 10k miles ago and this is driving me crazy so someone please offer up either a problem or solution

 

Did it start before or after the trans fluid change? First thought to me is it sounds like bad synchros in the trans since double clutching works. But, I would check the fluid is the correct type and is full. Also check master cylinder is full. Maybe just a clutch?