Hello and welcome to our forum.
Sorry to hear of the ongoing problems you are experiencing with your laptop.
Those temperatures are not good and prolonged use would cause the premature demise of your laptop.
However, overheating by itself does not prove an inherent defect and could be caused by either blocked grilles/fan or dried thermal paste.
Saying that, if Samsung replaced the entire mainboard rather than just the GPU then it is likely that the replacement board was also defective as the the affected GPU's are present in laptops in the field and also in spare parts.
If Samsung simply reballed a GPU onto your old mainboard then this type of repair is prone to failure and is not an acceptable form of repair considering the circumstances.
I would get in contact with Laptops Direct and would tell them that you believe that the mainboard in your laptop is reaching abnormal temperatures and that you believe that the board used to repair your laptop is also inherently defective.
They may tell you that your laptop is out of warranty and that there is nothing that they can do. You should tell them that the warranty status is irrelevant as you have six years from the date of purchase in which to bring an action against a retailer when the goods in question are inherently defective.
They may then tell you to contact Samsung. You should tell them that you purchased from Laptops Direct and not from Samsung so it is entirely Laptops Direct's responsibility to resolve the situation.
See what they say. If they say they will inspect it for a fee you should refuse and say that due to the "reverse burden of proof" then you will provide your own independent engineers report.
There is a step by step guide on this forum that will help you reach a positive resolution and that is here:-
post13.html#p13If you follow my advice in that guide then you will be successful.
I hope the above helps.
If you have any questions or if you need any advice then please let me know.
Good luck and best wishes
Paul
The Admin Team