I think the modules you are using are the same as Bruce sells, the RWS/TWS ones?
What are you using for an antenna and how long is it? Should be around 6.5 inches. Ground plane? Anything around that could be causing interference? A picture of the setup might help.

Can you post the code that is sorta working? At this point it could be a number of things. We have to rule out hardware or software.

Now try to tighten things up a bit.

Code:
TRAIN  VAR BYTE
train =  $B3
SYNK VAR BYTE
SYNK = $7E

SEROUT2 PORT??, BAUD?,[TRAIN, SYNK, DEC 23]
Code:
SYNK VAR BYTE
SYNK = $7E
MYVAR  VAR BYTE

SERIN2  PORT??, BAUD?, [WAIT(SYNK), DEC MYVAR]