I've had a similar problem with the cadence transmitter. I don't use the extender so therefore have to lean the transmitter out a little bit. Rarely it won't register a reading but usually if I just lean it a little closer and remove and replace the computer it works again.

I've never had a problem with the heart monitor. It does seem a little delayed but I don't care that much.
Quite frankly I think I can just about guess my speed, cadence, and HR by now. The computer just verifies that I'm pretty close.

One more thing, the temp seems correct in the garage or on a overcast day but in the sun it reads high.

I like the unit though. In the future however I think I'm going to get a gps map/speed unit

One more thing. I still can't buy the computer interface for the Sigma. Did you find one?