I really don't know for sure what you might be experiencing, but I've been using Audition 1.0 for a long time and recently upgraded to Version 3.0. While it seems that Version 3.0 does process information quicker, I also noticed that 3.0 slows my machine down quite a bit. I also get really slow performance when multi-tasking, if 3.0 is loaded up.
So, again I can't say for sure, but it seems from my experience that 3.0 hogs way more RAM than 1.0 does. It's a trade-off because like I said, 3.0 seems to process 24bit files faster than 1.0, but then it seems to bog down because of RAM limitations.
Honestly though, 3.0 doesn't appear to do much more than 1.0...which I don't think did much more than Cool Edit 2.0 (does Cool Edit Pro handle 24bit?). In the end, I'll probably just stick with 1.0.