Definitely fuel or the lack of... all of the suggestions above are plausible, so yes, please fill out your signature and carefully go through the checklist and look at the items there.
We don't ask for the checklist simply to cause you work; actually going through and checking all those items on your truck eliminates many of the everyday preventative maintenance issues that can cloud the problems you're having... in short, if you HAVEN'T checked those things in a while, it's overdue.