ePMP throwing HTTP errors

We have a 2.4 SM customer in NAT mode with a -66 signal and 30dB SNR, downlink MCS stays fairly high. However, the uplink quality in the test is hard to even reach 2Mbps. 

There is no other client on the same AP that is having issues with certain sites, but this just started this week; our customer is experiecning HTTP 403 and 500 errors on certain sites that worked fine before...sites that they need to run daily business.

I am going out to the site tomorrow morning and wanted to jump in on the forums and see if these errors have been experienced by anyone else before I troubleshoot the router, etc.

403 is the server rejecting the connection, 500 can be a lot of things. if your using DNS proxy or the end user, try to use public resolvers to see if that clears it up. also if you've got an upper range IP block check to see if the customers work network is blocking the ip range. some businesses have gotten lazy and blocked entire /8 ranges. if they are connected over a VPN, the error 500 can come from packet loss over the link. 

the uplink speed, if your using 10mhz mode with 75/25 split and a little noise, i'm not shocked by that, what is the clients uplink quality and capacity look like ?    if the quality is all over the board, i'd take steps to increase the uplink signal strength