8meg is definitely ADSLMAX in which case over the next 7/10 days your line will slowly stabilise. I actually found that my connection settled back at the original 1meg speed which I was receiving before the upgrade !!
As mentioned already not everyones line can cope with the higher speeds that ADSLMAX can provide. I also replaced my modem with a Netgear router which copes better than most modems.
This is a problem affecting many people who have been upgraded. For more info here's a really useful site:
http://www.kitz.co.uk/adsl/lowSNR.htm