Hey @V I K A S G A M E R Z!
Since you say that your PC is good and only "lag"s on TruckersMP, you have to differentiate whether it is due to your internet or the game itself. (Your own game is lagging/stuttering or other players are lagging for you)
TruckersMP can sometimes be a bit tricky, especially in busy areas like Calais or Duisburg.
You could try a few things in order to fix it:
Avoid High-Traffic Areas
Try avoiding the busiest zones if you're getting lag there. (Like Calais, Duisbourg in general and the C-D road, Coco Factory, Kirkenes,...)
Lower Your Graphics Settings in ETS2/ATS
Lower your general ETS2 Graphic Settings and lower the Draw Distance on TruckersMP (TAB -> Settings -> Graphics -> Draw Distance -> Low)
Checking Your Internet Connection
If you generally don't have a good connection, this can quickly affect TruckersMP (e.g. high ping). You can perform an online speed test for this purpose, for example.
Close programs that use your internet (e.g. streams, YouTube videos, downloads etc. or people in your household who also use the internet).
Connections via WLAN can also have a negative effect. A connection via a direct LAN cable is recommended.
Update Graphics Drivers
Make sure that your graphics drivers and game drivers are up to date.
I hope this helps!
Kind regards,
Leon