Could be a couple of things adding up, (or not) -- you might have one or more bad grounds, as well as a possible short, and/or wiring compromised within the insulation...
I'd start by checking out the relay box at the driver's left knee. Beware the typically rusty bolts/(screws?) holding it to the wheelhouse -- there's some of your candidates for a bad ground --.
Check and clean your fuse block (and underneath it) next...
...of course, it could just be something behind your instrument panel...
Had the same issue about 15 years ago. Had someone do exaust work. Had a loose wire for brake light short on muffler. Kept blowing a fuse and lossing dash and lights.
It only happened when the truck was running over 40 mph.