WNDR3400v3 slow wired connection

I recently upgraded my internet speed from 50mbps to 100mbps. Prior to the upgrade my wired connection speed to the router was always very near that 50mbps mark and my wirless speed was also very close (somewhere in the 30-40s).

After upgrading, the speeds directly out of my modem are actually higher than the 100mbps target, I'm getting 120-130mbps consistently when plugged directly into the modem. However, when hard-wired to the router, I am seeing a significant drop off. The wired router connection has never been above 60mbps. My wireless speed is about the same as what it was before.

I called support and they kept telling me that wireless speeds will always be less than what you pay for. He was not understanding that my concern was the hard-wired connection being half the speed that is coming directly from the modem. Then, he wanted to charge me $80 to try to "optimize the settings" remotely. I could go buy an identical router for less than that price and use the free trial support and have an extra router lying around (that can apparently only handle 50mbps incoming speeds).

Anyways, I was wondering if there were any troubleshooting steps I should complete before buying a new router. I've tried factory resetting the router, Downgrading and Upgrading firmware, different ethernet cables (all cables worked at 120+mbps directly to the router). Nothing can get the speed above 60mbps.

Thanks for any help that can be provided.