I've found the free tests at this site to be the best at testing your Internet speed. http://www.speedtest.net/ If you bypass your router, I seriously doubt that your true speed is different from what the test shows. If it's still slow I would ask your DSL provider to send someone out to show you on their equipment that you are getting what you pay for.
go into your dsl modem's line diagnostics and look for noise margin (aka SNR ) and attenuation. these relate to the quality of your dsl connection. noise margin should be over 12 db (higher is better), and attenuation should be under 45 db (lower is better). if you have good line quality, then the issue is probably with your software driver or modem's setup.
one more thing: you may have a good quality line, but if you're running too high a speed for the line, it will result in a bad connection (lots of data loss). for instance, running 6Mbs on a line that can only handle 3Mbs will not cause your DSL to run at 3Mbs; it may run worse than a normal 1.5Mbs line. so it's important to run only as fast as the line can handle. going beyond that makes things much worse.