It's definitely the case that you have a poor quality connection. I don't have a particularly good connection (although the quality is not bad) and in normal conditions I get jitter of only about 5ms to Japanese servers, which of course are located very far away from me. If you're getting 300+ms jitter from a close server your connection has serious problems.
I recommend you contact your ISP (and/or phone line provider if it's the regular broadband that uses a telephone line) and complain about the poor connection quality.
[edit] Just realised that your test was with a server 1000 miles from your location, but that shouldn't matter so much for jitter as you can see:
I recommend you contact your ISP (and/or phone line provider if it's the regular broadband that uses a telephone line) and complain about the poor connection quality.
[edit] Just realised that your test was with a server 1000 miles from your location, but that shouldn't matter so much for jitter as you can see:
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