slow application ('lag')

hey all!
i'm the kind of person who starts making games and has never got much further than the beta development phase.

i am now working on a game that's similar to doodle-jump. (the ipod app)
the thing is, i'm facing lag troubles. the game starts quick then gets all slow after 2 mins.
this is not the first time this occurs in a game that i made. it also happens in a platformer i'm trying to work on (which might just be ready in 2012 if i'm lucky.. LOL).

any ideas on what might me going wrong? could it be due to changing variables that get more and more complicating (like depth numbers that rise too high?)
i DO remove the movieclips that i no longer need.
thank you.

Doubt it will be anything to do with depth numbers. How do you put your games together? Do you use a lot of ClipEvent(enterFrame)s? Do you use one frame on the main timeline or do you have it looping over and over? Having broken loops or hitTests and such can also cause "lag".

If your game isn't that far through yet and you fancy, you can email me over your .fla and I will have a quick glance and see if I can spot some problems.