If you take your EVO into a Sprint store for diagnostics or repair, one of the first things the Sprint technicians are going to install after they receive it is an application called Retail Diagnostics. When they return your phone to you, they generally have removed that program from your phone, but Pactive73 managed to post a copy of the app after his phone was returned with it still there.
This Retail Diagnostics application runs a quick series of tests and reports back the battery health, charge, temperature, what radios are enabled or disabled, whether or not the device is currently provisioned, radio signal strength, and several other useful tidbits of information.
While not the end-all of tests for why your phone might be misbehaving, it does present much of the most useful connection diagnostic information on one screen.
Some interesting things to note on this is the application will block all calls while you're using it if the "Block Calls" box is checked, and it does not appear to recognize WiMax as 4G Enabled, although it will detect it as the connection type.
It's well worth a look if you're adding to your arsenal of diagnostic and debugging tools, although a word of warning: be careful about posting screen shots of any diagnostic output as your phone number will appear next to the MDN.
You can download the app at the link below.[xda-developers]