HP EliteBook 850G2 cooler upgrade

Hey there, I have an EliteBook 850G2 which is a fully loaded model, including a Core i7-5500u, 16gb of DDR3 and an AMD FirePro M4150. Now, the laptop runs fine, but the GPU starts underclocking at 75°C and drops from 715mhz down to 590mhz, might not sound like a lot but it is. I replaced the thermal paste with Thermal MX-6 but I still have this issue, and often, especially playing older NFS games, the CPU will hit 100-105°C and the GPU 95°C. Is there a compatible cooler from a similar HP laptop that I could install in this that is a bit higher performance? Or should I buy thermal pads and install them on the heat pipes to transfer heat to the bottom cover, thus increasing surface area?