Xbee Communication problems

Hi!

i´m developing a project that has 2 Xbees XB24-B on the respective shields attached to 2 Arduinos MEGA 2560
got the 1st on Serial 1 and the other on the serial 3.
. Im using the API1.

The thing is that i cant get full duplex communication.

I´ve got the code for sending and receiving under conditions inside the loop. But the only result is partial data loss and sometimes even total data loss.

Can somebody give some enlightenment on this issue =( =( =( =( =(

What is your addressing setup on the XBees (ATDH and ATDL)? Also what version of the firmware are you using (ATVR)?