Good dual band antennas

I'm currently trying to debug an issue with a TL-WDR4300 and I'm wondering if anyone knows where I can buy decent dual band RP-SMA antennas.

These looks like the stock TP-Link ones, and I have to wonder if they are listed at 6dbi if the 5ghz gain is lower.

On the other hand I've seen these listed as 8dbi on 5ghz and lower on 2.4.

The thing I'm trying to figure out is why my Netgear WNDR3700 can BLANKET the house at 19txpwr, but my TP-LINK TL-WDR4300 has garbage range at 21txpwr. Barely covers half my house. So my first idea is maybe crap gain on 5ghz with the stock antenna.