I wonder what the above is for.
the dir-655 has an uplink test that determines what speed it can upload. your wrt54g does not have this test.
if there is an upload issue with your ISP then it will cause the issue your having with your 655.
to test it, bypass your router,run a continual ping to someplace like google then upload a large file and do a bandwidth test. under normal circumstances this should not produce anything unordinary.
if your ping times jump to 500ms and your upload bandwidth drops way down, then its a problem with your ISPs upload link.
I am currently having this issue with my ISP and I had very simular symptoms that your describing.
If you are having an issue with your upload with your ISP you can still use your DIR-655 but will need to disable your QoS engine.
But it is still an issue you will want to address with your ISP.