Lots of folklore on this subject. The small print is that the 2.8 has a small chamber, gear impeller pump. In temps like you experience in Texas (I lived in Arlington for 5 years), and with a pushrod OHV engine, you might be better off with 20W-50. No overhead cam mobility to worry about, but with that tiny chamber pump you need raw viscosity and body in an oil which will fill the gap of wear, both in the pump and crank bearings. I've had Blazers and one Jimmy go past 250K with 2.8s massaged with Castrol or Valvoline 20W-50, didn't leak a drop or smoke ( except for two with bad valve guide seals). G'luck...Cal