R6700v3 New Firmware Slow Speeds

Must echo all the other replies here.  It seemed that lately my speeds on my r6700v3 had gone from 100/10 to 15/.5 and 4x my regular pings.  I tried restarting all the equipment from the pcs to the router to the cable modem, no change.  Plugged my laptop into the modem, and got the advertised speeds.  I found this thread and using others for some instructions downgraded firmware from 1.0.4.84 to 1.0.3.66.  I forgot to do the factory reset (with the reset button in back) and got confused that I now had 100/.5 with the same bad pings.  Finally realized:

******DON'T IGNORE THE POSTS THAT SAY DO A FACTORY RESET!******

After the flash of the 1.0.3.66 firmware and factory reset all speeds through the router from any device are now as advertised!

Unfortunate that we have to use an insecure version of firmware, and spend half a day troubleshooting.

Has anyone tried the DDWRT builds?  Does it solve these problems and how is the experience?

I saw that one message on these forums about the R7000 had the same issue and one of the posters noted that he just did a factory reset (without changing firmware) and it worked for him.  Anyone else try this?  It would make sense, maybe after the newest build was installed all we needed to do was a factory reset.  Again, if true, it's unfortunate that no one told us, and that all your settings need to be reentered.