Leaking, please help...

Gidgetwho

So we just got 8 BG 4.0s since we will have two in diapers soon and I've been using them on DD and we haven't had ANY leaks with them.  My 3.0s can't seem to keep up with her though.  In the 3.0s I have to change her almost hourly which seems excessive for a 19 month old.  Is it possible that my inserts are no longer absorbant?  Or is it more likely that I have detergent buildup and need to strip my diapers and then switch detergent?  I'm in the process of replacing the elastics in my 3.0s, is it possible that she seems to be soaking through them a lot faster because the elastic is not giving a good fit?  Any other possiblities?  Any advice?