High SPU usage

[greenseed]

We installed a pair of 100Fs recently, and mostly they are doing great, but I'm concerned that the firewall shows SPU at 70-80 during the day time, when sessions are at 5-6k and memory is at 20% and cpu is at 0% and bandwidth is only 20-30Mbps. We have very few security features turned on yet (no AV, filtering, etc). On occasion, some users complain that the internet gets really slow for them as well, though I can't be certain that is related to the firewall, the complaints did seem to start right after the firewall was installed. Something just seems off, and I can't quite put my finger on it. Any thoughts? What could be stressing the SPU so much with this low of usage?