Unfortunately packet loss is part-in-parcel of wireless network (or any networking for that matter but most prevalent in wireless). Your options are to:
- Try repositioning the range extender (a 1ft relocation can make a word of a difference)
- Try using a different Wireless Channel. (Most common on 2.4GHz Wi-Fi are 1,6,11)
- Try 5.0GHz if that's not what it is already using. (Try different channels here as well)
Beyond this there's not much else. Wireless isn't great for gaming. Powerline has its own issues that make it a hit-or-miss solution.
Someone else can follow up if I've missed anything else.