Is it a needed to open ports for Technicolor TG582n?

[#1]

So I've had a long running problem with some online games, stuttering in areas with a handful of people or more.
I never had to bother with port forwarding with my old dg814, I'm on 20 meg fibre now and got the Technicolor TG582n FTTC router, is port forwarding a requirement for normal gaming? 
Is it possible this stuttering (almost feels like my game connection is capped and any busy area just splutters to get enough data) could be caused by blocked ports?

[#2]

No. Issues with blocked ports would prevent connections. It wouldn't cause stuttering after connection. Do you have anything else running in the background that would use your internet connection?

[#3]

I don't, I've tried with 3 different high spec computers now and it seems to happen with them all.
Games (WoW/Tera few others) seems to run decent in outer areas but as soon as I enter a smaller town or whatever it stutters like mad, started about 6 months ago.

[#4]

That sounds more like graphics to be honest, is your card running hot? If you're not sure a program like GPU-Z will show you: http://www.techpowerup.com/gpuz/
If it is, first try hoovering it out (clearing out the dust in the fan and heatsink will improve the cooling no end, and hopefully stop the stuttering). If you do that regularly anyway might be worth turning down the settings in the game to see if that improves things - that'll also help confirm if it is the graphics card that's causing the lag).
Hope that helps.