CPU Bottleneck, what to do?

I had assembled a PC from used parts. I was recommended an i5 2400 to a GTX 980. But I bought the better i5 3470. I played long games like Fortnite (1.5 years) and everything went well with over 170 FPS. After Chapter 2 the game seems to be a lot more CPU hungry, because it just stutters, the imput lag is higher, despite 90FPS. According to UserBenchmark, CPU and GPU are on the same level. Then I looked with RivaTuner to see if I had a bottleneck and lo and behold: The CPU is consistently over 90% full (despite below 55 • C), whereby the graphics card with less than 50-60% (60 • C) is not really required. The stupid thing is that I bought a 144hz monitor and no matter what setting I don't get 144FPS: / What can I do to make games run normally again? New CPU? If yes, which?

I would appreciate any answer.

Specs:

i5 3470

MSI GTX 980

ASRock h61 mainboard (CPU not overclockable)

BeQuiet 650W

16GB 1600MHz RAM

EKL Ben Nevis

For 144hz you need a new CPU like a 9600k or Ryzen 3600

Can you get an i7 for the base, it should be around 50 euro.

Cpu upgrade 1230v2 ~ 30 euro

Would switch completely to ryzen.

A ryzen 5 1600af

board

Motherboard.

And then you have more fps ^^