That was in the Ford back in the the 1980s. I solved that issue by changing oil. I only mentioned my previous experience to hopefully read about what makes some oils resistant to the greater heat loads. Mobil 1 isn't cutting it in the Blazer.Are you saying the oil pressure goes to "zero" while stopped and at an idle after getting off the freeway? With that same oil, what's the oil pressure while cruising down the highway? Any idea what the oil temperature is?
What kind of oil pressure gauge does this truck have?