2002 Cadillac Deville over heating

I have a 2002 Caddie with a northstar motor, 8 cylinder. It was overheating on the highway, we repalced the rad cap and it seem to fix the problem for a couple of weeks. Then it started overheating more frequently and not just on the highway.

There is a new rad and thermostat on it. The rad cap is new. There is no visible leak but we are losing fluid some where. Only 1 of the engine coolingfans is running, the second is not wired to work at all. There is no evidence of a head gasket leak, in the exhaust or the oil. It does seem to continue to airlock when it overheats.

Thoughts?