GTA Online unplayable

[#1]

I’ve recently moved to Plusnet from BT, and stuck on ADSL as fibre isn’t available in my area. Ever since switching, GTA Online on my PlayStation 3 has become unplayable. Death-matches and races are impossible to be competitive in due to lag. Other players’ cars are jumping around the screen, and in death-matches I’m killed before the attacking player’s reached me on screen.
I’ve enabled Game Mode on my router, but the issue hasn’t improved. In fact, playing a death-match this morning it seemed to be worse.
It’s quite disappointing after all the positive things I heard about Plusnet before I switched. As an aside, general Internet speeds seem to be alright, but I don’t know enough about routers and network connections to diagnose/remedy the issues I’m currently having.

[#2]

Are you playing wired or wireless?

[#3]

Wired on ADSL.

[#4]

check routers ids log as it could be blocking packets.only way to disable it is type ids config state=disabled using telnet.use dmz for your console.upnp or port forward dont work well on technicolor router.if you still have lag then you need +net to check ur connection.

[#5]

How do I check the router’s IDS log? Also, I don’t have access to Telnet as I only have Macs.

[#6]

log into router>toolbox>ids.if you have only one console use dmz and turn upnp and any port forward rules off.gamemode? off, for me created lag it opens ports your xbox or ps dont even use i checked by telnet.respond to ping on.thats the best settings for that cheap router.if you have a bt hub i would use that.

[#7]

I found this guide (http://community.eu.playstation.com/t5/PSN-Support/How-to-put-your-PS3-into-a-DMZ/td-p/10655314) and followed the instructions and online gameplay has improved significantly.
I haven’t done any of the other stuff as—to be honest—it’s beyond me.