Problems playing Rocket League

[#1]

My family love playing Rocket League, but are having real issues with it at the moment.  The game constantly shows as having a poor connection to the server and there are loads of glitches.

To resolve this, we have set up port-forwarding, stopped playing it on wifi (which is ridiculously slow) and now connect using powerline adaptors or a very long cable, but there are still problems.

We're wondering if it's anything to do with upload speeds which are really variable at the moment.

Any suggestions would be appreciated.

Thanks

[#2]

I'd really appreciate it if anyone could help.

Is it likely to be better if I upgraded to Fibre Extra and, if so, can we try it out for a month before committing?  I don't want to waste my money if it will make no difference.