my phone hit a pavement and 3g/4g stopped working. next step? As I was cycling, my htc rezound fell on the pavement. The battery popped out.

There are few scratches but no visible damage. 

I start the phone and it's fine as long as I don't use data.
Once I use data, the phone uses "1" may be it's ev-do. speedtest shows 129 kbps down rate.

I tried flashing and installing a leaked ICS. that didn't solve the problem.

I would think that the damage was because of the physical shock of hitting the ground (nothing broke). so is there a way to diagnose it? to check if 4g is still working?
In the HTC Dream (G1) the UMTS radio (3G) is a separate board from the rest of the phone. While this is a Desire Z and I haven't had the opportunity to take one apart, it's probably very similar.

The 3G/4G daughterboard (or if it's connected, antenna) could have failed, cracked, disconnected or sustained damage in some other way. Software won't fix it. You have damaged hardware.