Connection Headache

[#1]

I recently changed from "your way pro" tariff because it would only allow upto 20GB monthly usage, and i was more often than not doubling that amount .
So i rang customer services and they put me on a different tariff with a 60GB monthly usage , and now i get awful lag whilst playing online with xbox and ps3  even disconnects from games at peak periods.
I have checked both my systems to make sure they are still in DMZ state,, which they are.
Interleaving was turned off when i joined a few years back but cant remember how you go about checking that yourself.
What annoys me is i asked if changing tariffs would affect my gaming experience and was told No.
Anyway i hope someone could tell me if different tariffs can cause Gaming issues. 

[#2]

Hi there,
It shouldn't do but depends on whether or not the game is marked in our traffic management systems (see sticky at the top of the gaming forum).
For details on different protocols and their classification on the different account types (you've moved to Extra, by the way) please see the page on our website here: http://www.plus.net/support/broadband/speed_guide/download_speeds.shtml

[#3]

Looking at the table listed above, it would seem that gaming should stay your maximum line speed, so its not a change of tariff that is directly lagging you.
When you first join alot of ISPs, they do stress tests on your line the first week to find the optimum speed for yout internet, and IIRC plus net does this. Therefore, when you changed tariff, it might have signalled for another stress test to update the info on your line. If it has been over 7 days, this probably isnt the case, if its within 7 days, maybe a mod could confirm this.