Why does Tomb Raider stutter during long ruin exploration?

While exploring ruins, I noticed a weird temperature split: Core 1 was at 62℃ while Core 4 hit 88℃, causing sudden stutters. I first tried increasing chassis fan speeds, but while overall temps dropped 2℃, the core delta remained over 20℃, which was a disappointing superficial fix. I entered the GamePP Hardware Control page and switched pump mode from Silent to Extreme, forcing speeds to 3100-3300 RPM. AIDA64 showed the core delta converged to 5-8℃, and HWiNFO64 confirmed water temps at 32-36℃.