saw your thread on Talk Talk
and as ive said before - ALL TT supplied routers are crap, you should use your own rather than TT supplied, they all have poor wifi and the Huawei HG533 (on Talk Talk firmware and connections) keeps dropping connections, i helped someone around corner who had TWO and both done the same, they had a Talk Talk engineer around who is bound to use TT hardware and the same thing happened....I went around, stuck in an old TP-Link they used to use and they have never had a problem since and this was 6 months ago.
youve had loads of routers from TT and they keep losing connection or have wi-fi issues, talk talk are famous for this and why they score poorly in customer satisfaction, the problem is (i think) that they have poor firmware in the routers but refuse to accept this and get the problem resolved, they seem to release a new router every few months (and/or firmwares)...no other ISP does this, so you need to ask yourself WHY...?
Ive read in two places (including TT Forums) that the D-Link DSL-3780 uses a Ralink RT63365
System On a Chip
the staff on the TT Members forum say that your noise margin is up and down and errors are high, sounds to me like you might have a noisey line and TT routers just can not cope!
get your own ADSL2+ router with at least 2 external antennas with a Broadcom chipset, ask TT to put you on a 9db SNRM and you will be sorted, after a month or so at that ask to be put on a 6db SNRM and see if it handle that...should do - also while on the 9db SNRM you could use Router Stats Lite to monitor your noise margin over time too see if there ARE any fluctuations and if so by how much, this is because the staff might just be seeing "Set Margins" by the DSLAM/MSAN rather than a minute-by-minute account, noise margins could be up and down just from flappy connections off a bad router...in that case there is NO noise on the line, but higher error counts could indicate noise on the line....