15 R3, CPU crazy activity, causes heat spikes and shutdowns

My Alienware 15 R3 is just out of a service shop, there was a fix for a number of wire repairs and a fixed short circuit on the gpu.

Since it got back, I installed new parts I ordered for it.

I do a fresh windows install. Got the latest drivers, software updates, bios update.

Here are my specs:
Processor Intel Core i7-7700HQ CPU @ 2.80GHz, 2801 MHz, 4 Core(s), 8 Logical Processor(s)
x2 Samsung Evo plus (500GB) *NEW
x2 32GB Corsair DDR4 *NEW
Nvidia GTX 1070

First things first, the CPU is in a constant state of panic - it jumps anywhere from 0.6 to 3.8GHz while idle, not performing any tasks. BIOS overclocking is disabled. Performance mode in Windows is also disabled. I am using balanced which allows the  CPU to work anywhere between 5%-100%.

If I start any taxing activity, the CPU goes into max overdrive and causes its temperature to skyrocket at 90+ °C. This includes downloads, any video games etc. If I launch a game, the heat rises and stays at 99°C causing the computer to shut off a few minutes in due to overheating.

The computer itself has been disassembled and re-pasted multiple times now. The fans are at full throttle. This is not an issue with lack of cooling capabilities.

The idle temperatures of the CPU cores range anywhere between 30-40 (with maxed out fans) which is acceptable, but if I launch any taxing activity the temperatures spike and you know the rest. Idle temperature of the GPU is also at 50°C, despite having zero activity, it also reaches the high 98°C.

Another interesting observation is that Core 0 and Core 1 are consistently hotter than Core 2 and Core 3. The latter two cores are cooler by an average of 15-20°C!

I've just about ran out of ideas for what this issue could be caused by. Any suggestions, ideas, comments? If you need more info just ask.