Problem retrieving headers when updating newsgroups. Very slow/ stopped download

[#1]

Ref using Usenet.
I can download a binary file quickly with no break-up in flow. That's all OK.
However, when retrieving a list of available headers, and then downloading the headers themselves, the download speed is very slow and mostly stops, and now does not complete. Very frustrating.
Please help.
I have contacted plusnet and they have been their usual unhelpful self. I have also contacted Thundernews.com.
I've tried both Forte Agent and NewsRover.
I can use NZB files to upload the specific headers and download the binaries all without problems and quickly. I just cannot get new headers to download for a general look at a newsgroup

[#2]

What account type are you on and am I correct to assume you're using Thundernews then? It may just be that you're using multiple threads to download message bodies, but only a single thread to download headers. That would certainly explain what you're seeing.

[#3]

Thanks for the reply.
I am with ThunderNews.com
The only details I can find are
30 GB/month
20 connections
SSL - No
Using either server eu.thundernews.com or us.thundernews.com
I'm sorry, I don't understand your comments about threads. Are these settings in Forte Agent?
Thanks for your help.