arp messages XXX is on but got reply.../multihoming problem

[Jer]

Dear all

I have a setup as follows.
4.9-REL

sis0: inside network 192.168.XXX.XXX

xl0: connection to RR commercial via DHCP
assigned ip  24.172.21.XXX gateway 24.172.21.219 nat'd

rl0: unused

What I want to do is plug in an RR home connection to the rl0 interface so 
rl0 would then look like
rl0: connection to RR home via DHCP
It got assigned an IP of 66.57.248.XX gateway 66.57.248.1

When I do this I get 1000's of
arp: 66.57.248.1 is on rl0 but got reply from 00:07:0d:aa:ec:54 on xl0

and the speed of the xl0 slows to a crawl until I unplug the rl0 NIC

how can I do this?

The default gateway I want is the commercial  account 24.172.21.219

Any ideas??

Thanks