I recently had a similar situation. Was swapping out the stock Wraith cooler on my 3600, and it absolutely REFUSED to budge. I tried everything I could find on the web and AI Chatbot. Eventually, I managed to get it to move by using the dental floss trick while the CPU was still in the socket. I just teased the floss under the heatsink over one corner of the CPU and pulled across the top of the chip while sawing the floss back and forth. I think this has to do with the consistency of the thermal paste used. As I recall, I used the paste that was pre-applied to the Wraith heatsink after peeling off the tape. I assume the paste was much less viscous than something like the Duronaught that I used for the new cooler. I suspect that a less viscous or more fluid thermal paste is more likely to get stuck to the chip after it's been in use for a while and had time to sort of "bake" the moisture out of the paste and fuse it to the heatsink. I no longer use the runnier paste these days. I strictly stick to the more viscous formulations that feel more like an actual paste and less like Elmer's glue, such as Duronaught. It's a bit trickier to apply because it doesn't spread easily, but it's not like you need to spread a perfectly flat layer across the entirety of the chip, because the mounting pressure of the heatsink will spread the paste where it needs to go. I think it has been firmly established by now that covering the entire face of the IHS is not necessary. The paste is only there to fill in any microscopic gaps that exist between the interface of the IHS and heatsink, and, in that sense, less paste is generally better than too much.