Imagine trucks now create a pressure wake that affects other trucks behind them.
Effects differ with:
Vehicle size
Speed
Trailer type (box trailers generate the strongest slipstream for example curtainsiders)
Distance behind truck the truck ahead of you
Impact on gameplay:
I'm pretty sure it'll help save fuel
Faster acceleration temporarily when entering someone’s slipstream
Most importantly cool overtakes like in F1, WEC or IMSA