All red lights on gauges light up when I hit a hard bump

WONDERFUL, don't you just love when it's a simple fix like that? Be great if all repairs were like that. Happy trucking!
Can you imagine if you took it to a shop for that? That will be $900 dollars. ( and what did that new U-joint have to do with the lights? HA)

 

I think the 387 has been notorious for this kind of thing. I've heard different theories and I've had a similar problem with my 06. It's been suggested that it stems from an earlier design flaw in the initial manufacture. It's taken 2 visits and about $1000 of bills to figure it out. And it still does it on occasion. Some of my gauges light up and the needles go haywire. Then it goes back to normal.
I would have Peterbilt do a diag, but you really need a wizard on electrics to maybe figure it out. Not all dealers are equal on this score. I'm going to take mine back once more to see. But it's certainly frustrating. The good news is that it doesn't do it as much as it used to. Just one of those crazy things.
Good luck.