I don't remember where I found this but it should help
1. Get your MSL, There are many ways, call Sprint, Download the app MSL Reader from the market, CDMA workshop
Faster 4G reconnect fix
1) Click on phone and dial ##DATA# (##3282#)
2) Click on "Edit Mode"
3) Type in your MSL code (see above if you don't have it yet)
4) Click on the menu entry "WiMAX"
5) Scroll down the list and click on "WiMAX_Scan_Retry(s)"
6) Enter the number 15 and click "OK" (This equals 15 seconds instead of 300 seconds)
7) Scroll down the list and click on "WiMAX_Entry_Delay(s)"
8) Enter the number 0 and click "OK" (This equals 0 seconds instead of 300 seconds)
9) Press the "Menu" key and click on "Commit Modifications"
10) Grab a cup of coffee, get a bite to eat, or sit back and wait for your EVO to restart
Testing:
1) Go to your phone's settings and click on "Wireless & networks"
2) Scroll down and click on 4G settings
3) Click on 4G to turn it on and wait for the status to change to "Connected to Sprint"
4) Without touching any of the menu items, cover the top half of your phone with your hands until the status changes to "Scanning..."
5) Uncover the top of the phone and count the seconds until it says "Connecting to Sprint"
6) Realize that you no longer have to cycle the 4G radio to reconnect