Slow domain authentication against 1 DC only.

Thanks for reading.

Domain is one tree in one forest in one site. Network hardware is robust and error-free. (2) win2k3 Domain controllers with dual quad-core xeon processors and 8Gb ram. More than enough disk space is present on each. Both servers located in same cabinet connected to the same access switch using same configured "switch-assisted load balancing with fault tolerance" across two nics for a 2.0G throughput. None of the interface ports connected to the domain controllers have any errors.

If I authenticate to DC1, applying computer settings takes less than 5 seconds.
If I authenticate to DC2, applying computer settings takes more than 1.5 minutes.

This behavior is consistant for most all of my users (about 300).

Netdiag and DCdiag on each domain controller are clean. Event logs have all been scoured relentlessly.

Both DCs have a global catalog and all the roles are located on (faster) DC1. Domain functional level is Win2k3.

Performance manager shows no bottlenecks.

Can anyone please suggest another line of analysis?