Hmm, first better to set it to WPA2 Only with AES. If your network can do it, no reason not to use it.
Second, I agree I would try turning off Short GI. It might lower your throughput, but if it lowers your error rate it will actually increase it overall.
Third, your signal levels are somewhat low. 38%? Do you get error rate and issues if you bring a laptop closer and connect at say. 60+% signal?