Netgear WNDR3400 experiencing bad performance after updt to firmware v50.

My NetGear WNDR 3400 N600 Dual-Band Router is about 18 months old. When I first got it, there was a prompt to update firmware, so I did. It worked fine for a little over a year, except once every couple of months it would drop the 5GHz broadcast (2.4 GHz would continue with no problem).

A few months ago, I checked for updates, hoping to fix the problem above. It said v50 was available. At this time it was running v38, so I updated according to the instructions. Afterwards, I started noticing significantly greater issues.

Now, 5GHz broadcast will stop within 24-48 hours after a reboot. This is consistent every time I reboot. About 72 hours after startup, performance (on 2.4 GHz) will slow down noticeably. This is especially for local networking between my three PCs, but also including the Web.

I've done a full reset more than once, reinstalling v50 every time. Are there settings to reconfigure which would help? Does the 5Ghz stopping sound like a hardware or software issue? Do I need better firmware from another brand?

Thanks in advance for any info help on this. Right now I'm using the wireless-g router built into my phone company's modem. It works ok, but I'd like to get the NetGear fixed.