What plan are you paying for? Looks like you might be on the 768 plan? I'm on 1.6 download 768 upload and I consistently get 1.5 speeds. Not sure why they advertise 1.6? Here's a test, I'm actually upgrading to 3 Mbps next week for an extra $2 a month.
As storm58 posted need to know what plan you are on. Best way to do that is to log into your router and take a look at sync rates.
At least here in Southern NH DSL speed has been pretty consistent. I'm on the 3000/768 kbps plan and typically get 2.87 Mbp/s down .73 Mbp/s up which when you factor in overhead from TCP/IP, PPPoE, and ATM is pretty close to maximum.