You're certain it's actually getting hot enough for the fans to turn on? They have a pretty high turn on temperature stock. Then again, since they don't come on with the A/C I don't doubt you.
The first thing I'd do is check the fuses and relays for the fans. Test the relays to make sure they're actually switching and providing current flow. You can at least rule out the fans and wiring since they do come on. To me it really sounds like a relay.
If they check out, check the coolant temperature sensor (located under the thermostat housing) and the wiring that goes to it. I believe yours is a 3-pin style, so even though your dash is getting a reading, your PCM may not be.
