OSX 10.7.5 / cubase 4.5.x asio issues

Yeah, I know, this is really old - I’ve been using Cubase mostly for arranging and making charts, so I have had no real need to upgrade,until I got a co - writing project that involves tracking real instruments — but ----

I am having asio overload issues with 10.7.5 and Cubase 4.5.x , using a firewire interface. When I run Cubase, it will work fine for maybe 30 seconds then the asio meter pegs and the audio crackles / drops out / slows down. If I let the Mac sit for a minute or two, the asio meter settles down, and it will go back to working right for a minute or two. The same project with the same audio tracks and same Vst configuration, in Garageband does not do this. I read that changing buffer may help, but there is no buffer adjustment for the (10 channel) firewire interface. I have checked my OS for start up items that may be hogging the CPUs, and dumped all suspects, removed start up apps like the wi fi for my printer and cell phone app (kies), but the problem still remains. Oh yes, and Wi fi is off, and I use one extension monitor. The FW interface is on the 400 bus and the file drives are on the 800 bus. And the Mac is a 2006 2.33 Ghz Core Duo 4 Gb RAM, 17" laptop. I tried a couple of projects that have more than 6 audio tracks, and I got the same problems. Ideas? Solutions?