my movie clips in my game are going to the wrong frames, plz help this isnt newb crap

ok, im making a game - ive made several before which worked pretty well but also had this problem. at early stages of developing the game it was fine. for example in the character movie clip's actions the 'jump ()' function made him go up and it would go to Frame 9 of the clip, his jumping animation. after a while, the problem came - now it would go to frame 10 instead. (the script still said 9) fine, we'll change the script to 'gotoAndPlay (8)', so it'll go to 9.
that was really just a quick fix. but then the problem came back later again. now it was skipping 2 frames - okay, make it 7. and so on, and now its 5 frames! basically my problem is this is now happening with not only every movie clip in the game, but also the main timeline! the reason this bugs me so much is that i only know how to do '_root.gotoAndStop (frame number)' or '_root.play ()'. i cant change the scene from a movie clip, so im making it goto a frame which then directs it to go to a different scene. this is causing LOADS of confusion and annoyance and is completely screwing up the whole thing. im sure im not the only person whos experienced this, and i really need to know why its happening or how to stop it.