I had the opposite problem with an 88 d100 and oil pressure.
I had to do a valve job on it, and found out that the original '302 (casting number) heads were cracked. This was a roller lifter engine, back then I didn't know that the '302s had fatter pushrod holes than earlier 318 heads. I had a set of older 318 heads here and figured "hey it's a 318, any 318 heads will interchange" but no. The sides of the pushrods were binding in the too small holes in the heads. (Probably '163 heads, which seem to be the most common ones I tend to get my hands on)

The roller lifters being taller changes the pushrod angle. I got it all back together and started it up and no oil pressure when I had fantastic oil pressure before I swapped heads.... I didn't understand why at the time, as I had done head swaps on 318s before that with no issues.
But this was my first roller motor I had ever been into. So I wound up paying $400 at a junkyard for another set of '302s (this was back around 1995) and those heads were hard to find back then. Plus the trip thru the machine shop to be sure these weren't also cracked.
I ended up doing a complete overhaul on that engine, before I was done. That was the most expensive 318 I ever had.
That doesn't take into account all the problems id had with the throttle body efi system on that truck. (1st year for that setup)
I'm just glad "that" system wasn't around long-- story for another time