If you mean by tech support via email, I too have not received the best feedback from them. I always recommend to people to phone contact DLink support, and not email as email is a low level or 1st level support and only seems to give basic information, when they do. Any more problematic issues that can not be solved here in the forums, should and probably can be resolved with level 2 or higher phone support depending on the problem. Most issues regarding set up and trouble shooting can be done here in the forums, however when all troubleshooting has been exhausted, then phone support is the next step. I consider the forums much like email support, however we strive to be most helpful and provide seamless support as far as possible. We've done what email and level 1 phone support should be doing, however when we can't resolve it here, theres no reason, IMO, to contact email or level 1 phone support. We've already done what they are going to ask you. So why bother with those levels of support. Level 2 or higher is needed.
However it seems we've narrowed down part of your issue here and seems to be related to external conditions for the most part. I believe D-Link products work well out of the box. It when they get in to external environments and conditions that problems can arise, with ANY wireless product, D-Link or Non D-Link.
Good luck and hope it all keeps working well for you.