I've never played any truck simulators and never will, but I'm pretty sure Ambient Occlusion would need Depth Buffer access. Make sure you have that.
~ I haven't used ReShade's AO yet, so this is conjecture.
The depth buffer in Truck Simulator games is turned upside down when using DX9 so any AO or DOF etc will not work properly, you need to use the OpenGL API to successfully use the Depth Buffer I would suspect. You also need some level of experience with using the Reshade Mediator tool or knowledge of the setup for those effects as it can take some time and tweaking and a lot of people give up or cant find the right settings.
Thanks for the reply :) : i've found about the manual flipped depthbuffer in reshade.me/forum/shader-discussion/601-manual-depthbuffer-flip?start=24#12477 but cannot understand very well what lines in the code and/or where is it the .cfg file to try to solve the problem.
Sorry for my shitty english...
Download the latest version of Reshade they have an option in there to flip the buffer.
the link http://reshade.me/
It's under Globals in the Reshade Assistant, this will save you time trying to modify Reshade.fx :)
And it's called: Reshade Depth Input Is Upside Down.