First question answer: if other players are if it caused an accident
be disturbed, you can report from this website: https://truckersmp.com/reports(you need
evidences)
Second question answer: when there is an incident you can report guilty person in- game, if your report not been seen and if you have proof, you can report guilty person in website
if your truck slow, maybe matter of the engine power or maybe engine failure, if engine failure go to service and fix your truck
Third question answer: you do not need evidence in the in-game reports because of report guilty person in-game, game moderators can see the accident in history (admin panel)