A speed test http://www.thinkbroadband.com/speedtest and post the results link might help...
e.g. if the tbbx1 test is slow and graph bumpy it suggests an issue, particularly if httpx6 is a good straight line
To know if its the Wi-Fi you need to test on another device that has Ethernet.
Some devices have a tendency to hop between 2.4 and 5GHz, so suggestions to name the channels differently might help e.g. I've done this and the phone only knows about the 5GHz credentials to stop it wandering around
Also different routers have different antenna so it sounds odd but rotating or moving the router a little might help, i.e. finding optimum orientation for where you use iPad the most.
Another possibility is that with older iOS the iPad was happy, but there have been versions of iOS where people have reported issues after upgrades so its possible that the Wi-Fi is fine and the iPad is playing around.