I was trying to set a WR on Utah River Rally and I noticed how some guys were using lower fuel levels and different body styles (One guy had no hood, like without crashing it, to save weight). The car configuration isn't there when I'm in time trial mode. If you can help me out massive thanks.

To do that you will have to make your own configuration in Freeroam and save it, then it will appear in time trial mode.

You can "create"/ modify cars yourself in BeamNG.drive itself, the use of "custom" vehicles is allowed as long as it is 100% vanilla BeamNG.drive. Here is a picture of the window you need to open to customize vehicles:

You can make custom vehicles seeable for you for time trials if you go to options --> User Interface --> show custom vehicles in vehicle selector.

Thanks my guys. I'm gonna hop on Richard Burns Rally tomorrow to get Northumbria World Record then I'm gonna smash Utah