I am having the same problem. Recently bought the Netgear WNDR3700 router attempting to fix a Logitech boom wireless issues, it didnt. The DLINK DIR655+ worked great at translating ports, it was done under the configuration setting "Virtual Server" allowing a public and private port to be identified. I could not find such a configuration setting in the Netgear WNDR3700. I tried to to see if Port forwarding would translate, it didnt..
When configuring port forwarding on the Netgear using a starting port of 80 and an ending port of 8081, it states, "The specified port(s) are being used by other configurations. Please check your configurations of Remote Management, Port Fowarding, Port Triggering, UPnP Port Mapping table, RIP and Internet connection type". When examining these configurations on this new router, i could not find any other use of port 80 or 8081. If switching the starting and ending port around, 8081 and 80 respectively, it states, "Ending port value should be greater or equal to Starting Port Value".
Anyone know a solution? For being their home networking flagship offering (and expensive) router, i would expect the Netgear WNDR3700 to handle something as simple as port redirection?