3310 version 5.13 problems encountered

hi, i'm a new member and needs help, infact i don't understand most of the technical terms as I went through the forums such as; "flash." Anyway, here are the problems i encountered with my month old 3310 version 5.13 cellphone as follows:

1) seldom send or receive text message even w/ one (1) bar
signal while other 3310's of lower versions (i.e. 4.+ to 5.03
made in China w/ same signal strength experience no
problem)
2) Most often, my cellphone do not have any signal at all.
3) long message sending time compared to other cphones

Note:
I only experienced the above problems when I'm at my work
station which is about 21kms from the nearest cellsite.
However, when i'm within the city to where the cellsite is
installed, the foregoing problems do not occur.

Will anybody help me please?

Edlopz