I know Metropcs.com has a coverage map, but it doesn't show the 2G, 3G coverage areas. I thought this might shed some light. I don't know how accurate this is, but here are the links...
Coverage Maps | 2G-3G - USA - Metro PCS | Sensorly
Coverage Maps | 4G - USA - Metro PCS | Sensorly
Coverage Maps | 2G-3G - USA - Metro PCS | Sensorly
Coverage Maps | 4G - USA - Metro PCS | Sensorly