Update: EVGA said that they would help me out with this.  I appreciate it.
 
My question is, how should repeat RMA's be handled.  Should the customer pay for shipping again or should EVGA cover the costs?
 
I bought a Bstock 3080 XC3 on 9/3.  I was thrilled as I've been wanting a 3080 for my daughter for a while now.  I put it in the test PC, but noticed that the performance numbers were about half what they should be.  I looked at GPU-Z and saw that it was thermal throttling(VRAM reaching 110 instantly.) really badly as if something was wrong with its thermal pads. I asked around and it was suggested to replace these pads, though nobody seemed to have the measurements for the XC3 model.  I read elsewhere that thermal putty can and is used to bridge the gap in some places.  
 
I bought all the materials I thought I'd need.  Replaced everything to the best of my ability. Put the GPU back in the test PC.  It ran even better than expected and I was thrilled, but then the GPU suddenly died a few hours into testing. I tried the GPU in a few different computers we have around the house, but none of them would so much as power up with the GPU attached.   
 
I had read that EVGA does not void the warranty over changing thermal pads. I could not find all of the original thermal pads to put back on the GPU prior to RMA, so I RMA'd it as is.  I paid shipping.  I was charged for new thermal pads.  While I wasn't excited about that, I understood that the product was not in original factory condition(Though that condition was unsatisfactory.) I should have RMA'd it prior to attempting to change thermal pads.
 
So today I got my replacement 3080 XC3. 1 month and 1 day from the original purchase date.  I was informed it had a different serial number, so I assume the entire GPU was replaced.  Popped it into my test PC to begin testing.  Things went well for about 2-3 minutes, performance where it should be for stock thermal pads.  Then, the GPU started hanging.  I updated the driver, but kept getting weird BSOD with artifact all over so couldn't read it. I figured enough with windows PC.  I popped it into a Linux PC.  No luck there, crazy memory errors on bootup, not able to complete boot.  Tried it in my daughter's PC(Switched it out with her existing GPU) and it did boot up, but quickly gave me a VIDEO TDR FAILURE BSOD.  After that, the PC would not post with the GPU in the PCIE Slot.  It would turn on, but not post.  Popped it back into test PC.  Same thing.  If it's hooked to the PCIE slot, no POST.  It powers up, all 3 fans spin. EVGA lights up.  But computer itself won't POST. It doesn't seem to have a catastrophic power problem like the previous bad GPU as again I can leave the 2 8-Pin PCIE cables attached to it and boot the PC up fine so long as it is not plugged into a PCIE slot. 
 
All PCs used for testing have high end GPUs and once again functioned perfectly prior to and after testing this 3080 XC3.
 
 So 2 part question here. 
1) What if anything can I do to troubleshoot now?
2) At what point should I not be asked to pay for RMA shipping anymore? 
 
I am getting frustrated at the amount of time and money I'm spending on a product that is supposed to function right out of the box.  I realize B stock items are refurbished, but I've never bought refurbished items of this quality before.  Maybe it's just bad luck?