Many thanks for your reply. We've alternated back and forth between the original cable and the Cat5 cable a number of times and each time the results are the same. Original cable = good, quick data transfer, Cat5 = very slow transfer. We were very careful to make sure the connectors were wired correctly as per the original cable... same result. It's quite baffling for us. Short term, until this problem is resolved, I've had to move the hygro/thermo unit back to a less than optimal position solely to allow use of the original cable.