Questions about the AC750 WiFi Extender.

I bought an AC750 Extender years ago to use for my previous router and it worked great. The occasional hiccup here and there but was usually fixed with a simple unplug and plug er back in trick. We got a new router and the wifi was great (surprising given that it's spectrum) but then I switched rooms around, now located in a room that's a floor above and also the furthest from the route. I thought, "No problem! I'll just use the extender!" And once I got it reconnected I started to try to use it and now my connection is dropped every 10 mins and I have to fight to reconnect only to be dropped again, over and over. I have yet to see it work as good as it did before. Any solutions to this or anything I could do to help it in anyway? Preferably a solution that's not me buying their most expensive newest extender. Thanks in advance!