Seems like truenas boot params can be altered with midclt call.
You can check your additional params with midclt call system.advanced.config | jq -r '.kernel_extra_options'. Mine already shows pcie_aspm=off. If yours doesn’t, you can alter it with midclt call system.advanced.update '{"kernel_extra_options":"pcie_aspm=off"}' and then reboot. All credit goes to this post.
Disclosure: I never altered boot params (in truenas). You should proceed with care. And perhaps make a clone of your current bootenv before changing the setting. Or just wait for the advice from more seasoned truenas users.