Wi-Fi Weak and Dropping Signal

I'm having issues with my iPhone 6. I'm relatively tech savvy so I've tried to trouble shoot this as best as I could. I went through all the standard network setting resets and restores with no effect. Here's what's happening:

The wifi signal is often weak but it's worse than that. The phone will constantly drop and reconnect to networks as well as cycle through different signal strengths. Other times no networks will appear at all and when my network finally reappears it won't be able to connect. It only really works best with a direct line of sight to the router but even then there's no guarantees. I had thought this was an antenna issue so I took it into a local repair shop and had the antenna replaced but there's been literally no change. I'm curios if they actually replaced the antenna or what.

The worst part about all of this is that the phone will be mostly fine for a little while and then randomly the signal will start to drop until its gone altogether. I spend so much of my time looking to connect to connections that I know are there but my phone can't see or connect to.

So my final question is. Is this likely an antenna issue or is there possibly an issue with the wifi chip itself. I haven't been able to find anywhere what the symptoms of a faulty chip might be so I'm not sure. What's my best option at this point?