I was having the same problem this weekend. I'm running DHarveys ROM too but don't send picture messages that often. I called alltel and and here's the settings they gave me that are working:
Gateway: mms.alltel.com
Port: 80
Server:
http://mms.alltel.com/servlets/mms
Size: ~300K (on my phone 292K was the closest)
WAP: 2.0
Make sure you can send text messages, and connect to the Internet. If this doesn't work, call them after you make the changes to have them reset your phone in the message system as u2gator said.