I have heard that claim many times... every single time when I investigated it wasnt true and came down to user error (or a lack of understanding in the mechanics of the GC)... Probably 200 times in my career as the guy consultant people call in to fix other peoples mess.
Pbviously in your case I cant say much more without seeing the code or knowing more of the problem... but not once has the GC ever actually turned out to be the problem in the end.