macos - iMac 27'' late 2009 with GPU problems gets fixed by reinstalling Mac OS, what can be really happening? - Ask Different
Amazon.com: Genuine Graphics Video Card for Apple iMac Late 2009 A1311 Core 2 Duo 3.06 21.5 Inch Desktop PC MB950LL/A MB950, AMD ATI Radeon HD 4670 GDDR3 256MB, MXM VGA Board GPU
iMac Late 2009 Graphic Card issues - Apple Community
iMac Late 2009 21.5" GPU upgrade - Apple Community
Upgrading an iMac GPU for METAL Support! Late 2009 – Mid 2011 Models - YouTube
GPU ATI 216-0732026 Graphic Video IC Chip for iMac 27" A1312 - Late 2009 (EMC 2374)