Have you tried Starting up in Safe Mode? (What is Safe Boot, Safe Mode?)

This is not a guaranteed test, but video issues that disappear in Safe Mode are often hardware related, so if yours do disappear, rerun AHT's extended test in loop-mode (control-L) for at least 5 loops.

Please keep us posted.
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In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire