I am having same problem after new patch. I’m using 1080ti and it will stutter dropping frames down to 10. Its very hard to race when this happens. when it runs smooth I average 99 fps on a ultrawide.
I haven’t ran afterburner yet to see what the specs of everything is.
same for me , since the patch more stutter 
i7 980x , gtx 1070 , 12 Go de Ram.
but it seems the game doesn’t crash anymore (I added 4 Gb to pagefile)
After new patch game is super smooth. I run couple time one race in carrier mode, 2/3 race in rivals mode (all races about 2 hours). But when I go to another rivals race, when I choose the car - CTD.
I5 6600K @ 4,4GHz
Kingston Fury DDR4 16 GB ram 2133@3000 (max used about 10GB)
Gtx 6600 6GB overclocked too (afterburner says 5813GB graphic ram used - but when CTD it was about 4800GB)
I don’t use page file.
Nvidia driver 388.00
All settings ultra and 4AA 60fps v-sync on 2560x1144
While overall the game is performing better, there is definitely another issue here. Here are the issues that I am having on PC:
- Browsing the car list there is a mismatch between the car pictured and the one actually selected. Too long and this will cause the game to crash (much in the same way it did before the patch).
- In Free Play, I can tune about 4-5 cars before I can no longer run any test laps without extreme drops in frame rate (from 60 FPS v-sync locked to under 20). I have to leave the game and eventually reboot the computer, as simply restarting the game and Xbox services no longer does the trick.
- Working in the livery editor, I usually have to restart after 1-3 cars (depending on the number of layers used). The game ends up stuttering and freezes. I can wake it up 2 -3 times by hitting the Windows key, but the game eventually locks up if I am unable to exit.
- After crashing, and even after shutting the game down normally, the Chevrolet Monte Carlo Forza Edition will be my selected car at the next launch whether on the PC or Xbox. This is very frustrating. Especially since going back into the garage will lead to another crash.
- Some liveries are not showing properly. I have to reload the livery or restart the game to see them properly.
PC Specs:
Windows 10 version 1709
Asus Z170-A
Intel i5-6600K
16GB (2x8GB) DDR4 2400
EVGA GeForce GTX 970 4GB (04G-P4-2974-KR)
Asus VE278H 27"