Hey guys, my boss has a 1997 f350 with the 351. It is obd1. I'm assuming its an old fleet vehicle. So the issue I'm having is quite possibly electrical. For some time the truck has done this thing driving down the road it will shift very hard and seem to enter a "safe mode" the speedo also quits working. We figured out by smacking the dash real good that everything will start working properly again. I'm at a loss here. I wanted to do a speed sensor but that has been done. I'm unaware of what else could be causing this. Perhaps a loose connection in the dash? Has anyone had this problem? Where should I start looking? Thanks in advance guys. The boss owns a number of fords so i wouldn't doubt that I'll be on here alot more.

Edit: the dtc code is p0780 shift malfunction. Lol like I didn't already know that.

 

Looking at this link, it seems the tranny needs some service done to it.
Ford P0780 OBD/DLC Error Code - Shift Error

 

Thanks, I'll see what I can figure out