Could be that the AP you're connecting to is sh1t, could be a raft of factors...
Plenty of folks connect to 5Ghz without issue, even in this very thread....
Remember that although 5ghz has better throughput, it also has much less range (esp. the older forms) than 2.4Ghz.
So make sure you're not expecting better performance than 2.4Ghz at 2.4Ghz range.
Oh & of course confirm that the AP is dual-band, & ideally simultaneous dual-band (i.e dual radio).