John has DSL and he's frustrated how slow it can get throughout the day -- often slower than dial up! Even worse -- he's being stonewalled by the national support center of the ISP. Leo recommends running the SpeedTest by Broadband Reports. Internet speeds are not consistent, but DSL should be more consistent. But if they have more customers than bandwidth, this can happen. It sounds like John's ISP is buying bandwidth and they simply don't have enough to go around. But it could also be bad routers and software. If they promised him a service level agreement that guarantees performance, then he has them over a barrel.
According to the chatroom: If they say they can only support SpeedTest.net, they may be messing with the results by prioritizing his traffic during the test, to yield a phoney result. John should use a variety of online speed test reports and then he'll get a better idea of his actual speeds.