Slow internet speeds

I have an ASA5505, and we are connected to a PPPOE connection through Bellsouth or ATT with a 6Mb business connection.  During the day the internet speeds will get extreamly slow  - down to 150kb for download speeds.  Most of the time I will reboot the ASA and DSL modem and then everything is ok for a little while and then it slows back down again.  I've tried talking with Bellsouth/ATT but thats like talking to a brick wall.  All they say is unhook the modem and hook it to a PC and then test the connection speed.  Which of course works just find and I get the full download speed.  So any help is trying to trouble shoot the ASA would be great.
It could be a hardware issue with the ASA.  I also have ASDM running but I'm no means an expert in that, I'm more of the command line pig when configuring the ASA.
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winstonboltConnect With a Mentor Author Commented:
Found that it was my backup servers causing contention of the network with their offsite stoarage, they use aspara to transmit the data offsite, which uses a % of bandwidth.  Dialed it down/turned it off and I was good to go.  thanks for all the help.
For startes, having a 6mb "business connection" does not mean you will get 6mb of throughput on your downloads. Is your internet a dedicated circuit or shared with the local ISP node? Virus scans? P2P Downloads? Excessive LAN broadcasts? Just some ideas...
May want to look at your CPU usage on your cisco firewall, could be taping out.
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winstonboltAuthor Commented:
Its a dedicated circuit - no lan broadcasts, no heavy downloads, etc..  It between the ASA and DSL modem.  I've taken the whole network offline except for 1 PC (my laptop) and still have the same issues.
Last thing to do to rule out the ISP would be to call and have them watch your network's utilization, latency, and packet loss.

No packet loss from the pc to switch, switch to cisco? If you have managed switches how does the duplexing look? On some Cisco devices if "Auto Negotiation" fails it automatically sets the duplexing at 10mbps/half duplex
Have you checked MTU and MSS on the firewall and and any routers.    You could be hitting a fragmentation issue.   Also, you can try turning off the class inspection for DNS.  This can also cause slowdowns for no reason.
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