The gas truck version is a synthetic and the maximum viscosity is 5 w 30. Personally, I don't feel comfortable using that on a high mileage engine.
I read lots of reviews of the T4 and it's well thought of in the Jeep Inline Six 4.0 liter crowd. Some reported the internals of the engine was still clean after considerable mileage. The general consensus was that the older engines benefitted from the zinc in the oil to reduce wear.
