The first thing that I see is you have SERIN and SEROUT on the same pin.
Code:
SERIN PORTA.3,

SEROUT PORTA.3,
I have never tried A4 for serial
http://www.picbasic.co.uk/forum/showthread.php?t=562
You may have to use another pin.

Right now do not worry about TRISA. The SERIN/SEROUT takes care of that.