@phil.davis:
You have set an "upstream" gateway on your LAN. Actually there is no gateway on a pfSense LAN, it is the WAN that has the gateway out to the internet.
Interfaces->LAN, change the gateway to none and save.
System->Routing - delete the gateway for LAN, and set the WAN gateway to default.
Firewall->NAT, Outbound - set it back to Automatic.
Now pfSense will understand that LAN is an internal network and WAN is the way out to the big bad internet. It will auto-generate NAT rules from LAN to WAN.
Nice one. Didn't catch that when I looked.