Alltel Roaming Issue

[Fire25]

Got a new tp under warranty and phone will not go out of roam. Took it back and the techs at alltel/verison said phone was broke and had another sent to me. Same problem with that phone. Newest rom update came with it. Will not program *228 have to do it manually. Seems when the signal strength is not good it switches out of roam but when Im some where its good goes into roam. All programming for area correct. Any help??