Eric.
Owing two machines running Debian Wheezy 7.5.0 (one of them is AMPRNet gateway, another one, just desktop PC connected bidirectionally to 44net world through the first one)... I wouldn't forget explicitly setting up MTU 1480 for tunl0 interface.
ifconfig tunl0 $AMPRIP netmask $IPMASK mtu 1480 up
Best regards. Tom - sp2lob