gpu Weird stutter after GPU upgrade

[AnthonySimek]

I recently purchased a new GPU (EVGA RTX 3070Ti FTW3, unfortunately from a scalper for around 1300 Freedom bucks) and I have a weird issue. 
When playing a game like Forza Horizon 5 the game sometimes stutters. When playing and driving around the game randomly drops FPS for about a second or so and then gets back to the maximum framerate. At the same time, the GPU usage drops to about 70%.
The temperature looks to be no issue, GPU stays around 70-78 degrees.
What I thought about is that the PSU can't provide that much power when the game needs to load new assets and drops the power to the GPU, but I honestly can't tell even from the graphs. 
The GPU at max pulls about 300W, the 5600X pulls max around 80W so the 650W PSU seems to be alright for the task even though I probably should get a better one. 

Any thoughts would be much appreciated.

[RTX 3090]

28 minutes ago, AnthonySimek said:

What I thought about is that the PSU can't provide that much power when the game needs to load new assets and drops the power to the GPU, but I honestly can't tell even from the graphs. 

Run AIDA64 free trial, and monitor the volatges and look for dips

 

29 minutes ago, AnthonySimek said:

5600X pulls max around 80W

Don't forget motherboard, USB devices etc. Motherboard probably takes a good 30-40w, USB devices is the Amps x 5, so a 2 Amp device would take 10w. SSD/HDD probably take another 10/20w, and this all starts to add up

29 minutes ago, AnthonySimek said:

650W PSU seems to be alright for the task

650W does not mean 650w across any rails, 350w could be for a certain rail, lets say 12v, and that might be getting maxed out. 

[AnthonySimek]

@RTX 3090I hit the system with Furmark GPU Stress test and Furmark CPU Stress test at the same time and saw a dip in GPU Voltage after having the CPU stress test as a focused window. When I focused the GPU stress test window everything was fine.
When I hit it with the System Stability Test in AIDA64 with CPU & GPU, the system ran completely fine. The voltages looked fine too (atleast to me). 

Any idea what could be the problem? 

When I ran RDR2 the other day, everything was fine, but Forza still has the same issue.