LÖVE

I've been working in a rhythm game now over a year now, and my pc gpu broke where i was doing the development of it, the game used to run with no perfomance issues, but now on my new pc i have been able to see stuttering & worse 1% lows, and i noticed that lines up with the garbage collector cleaning the memory, my question is what do you recommend to fix this sort of memory leak or whatever is going on behind it?
the weird thing is that the new was supposed to be stronger than the other one.
my guess is the cpu, i want a bit of advice to optimize bc is better getting the thing optimized that making the players suffer it, taking note that i want my game to have tight response windows.

dead pc:
cpu: i5-4400S (4c/4t)
gpu: amd radeon xfx hd 6850 120w (this is what got fried)
ram: 8gb ddr3
hdd: lexar 120gb ssd & western digital blue 1tb hdd

new pc:
cpu: amd fx(tm)-8350 (8c/4t)
gpu: nvidia gtx 1050 75w
ram: 16gb ddr3 (it was 8gb but it has the ram of the dead pc since they were good)
hdd: Adata su650 120gb ssd & toshiba dt01aca100 1tb hdd

What profiling tools or other stuff to do performance analysis do you guys recommend?

I've found jprof to be a good tool for measuring code performance and memory consumption.

What OS is it? I borrowed a notebook for some time and it came with Win10 -- I could not stand it after a couple of days, so much bloat and so many little processes that suddenly eat up huge amounts of CPU.
I had to downgrade to 8.1, which is my favourite. Then everything turned out great.

How did you narrow down that it's the Löve runtime that's causing the CPU slowdown, and not something else?

I like ivan's profiler, myself. It's a love script that measures time spent in various parts of the code. Check it out!

Have you tried running other love programs? Might be worth doing to see if its some issue with love itself, or just the code of your project.

According to some CPU benchmarks I googled, your Intel CPU is almost 15% faster than the AMD CPU you replaced it with, when doing single threaded work.