is it a stock rooted rom or just the stock rom? (in other words did you flash a different stock rooted rom after you rooted)
the wimax radio is located here in the first post .. just flash it
http://forum.ppcgeeks.com/cdma-htc-e...651-5-ota.html
you can try to flash a different rom all together // most of them include uptodate radios and such
edit: im not sure if the wimax radio is for that rom specific or not .. you can look around and see if there is a post for just the wimax radio zip itself .. that link was the first one i saw with a wimax .zip stand alone
did you try the PRL update .. the PRL and PRI are 2 different things
to update PRL go to menu > settings > system update > update PRL