After correcting my routing setup, I have SLIP and PPP both working as expected over a direct serial connection.
I had to adjust the NAT setup within my home network. For now I used ipnat on the NetBSD slip server. I also had to add an additional static route on the client to the address of the network card on the server with the ip address of sl0 on the server as the gateway. Thanks to everyone for your help in sorting this out and patience as I tried to determine the problem.
