It is just your last post confused me as you only gave information on your graphics card, that made me question if it is/was the GPU.

As my search on the CPU gave that like which seems to say 80c is within the thermal maximum.

Dell will say your warranty is invalidated if you pretty much do any hardware modification, considering you have already modified/upgraded the graphics card, you have already crossed that bridge. There is of course more risk of damage in changing the CPU cooler and fan.