Help fix a networking issue

I have a new Lenovo laptop which I'm having networking issues with. It takes a few hours of use to show up, but once it does it starts having constant trouble connecting to the router. If I run ping tests to [login to view URL], I'll get quite a few non responses or response times of say 700ms. I'm running 2 other laptops on the same network that have no trouble at all, including another older Lenovo right next to it that reliably gives responses of 1ms, with the occasional longer one of say 40ms. This is with a clean Lenovo factory install, no laptop firewall. I've set up Wireshark, but don't understand the data it gives. If I run windows diagnostics it sometimes says all is fine, and then sometimes spots a problem, but dos nothing more than an adapter reset. I've had the laptop back with lenovo, but they couldn't recreate the problem, and eventually just replaced the Wifi card and returned it, with no improvement. It works fine with a wired ethernet connection. The router is a Draytek, and I'm connecting via 802.11n. I'm running a second wifi zone off the Draytek and I get the same problems with that. I've plugged in a separate USB Wifi dongle to the Lenovo and had problems with that too. I've been using Pingplotter and I might be fine for a couple of hours but once the connection problems start, I'll get non response fairly solidly, with occasional breakthroughs of connection. What i might sometimes find is that the connection issues are fairly bad on pingplotter and maybe a chrome browser, but a different browser is connecting quite well. I'm seriously at a loss here, and suspect its a software/driver problem or driver advanced configuration, but I have the latest driver for the Broadcom 2x2 11a/b/g/n wireless LAN PCI Express Half Mini Adapter Card. I'm connecting via an unencrypted connection in a location that's several hundred yards from the nearest other wifi. I'm about to go on holiday for 2 weeks, and want it fixed before I go as I need to have the laptop available for on-call issues. I'm in the UK, so I need it fixed by noon 25th April GMT. I guess I'm going to need some interactive assistance and Skype comms to diagnose and fix this, which will need to be 9-5 UK time on 24th or 9-12 UK time on the 25th.