I replaced the connecting rod and main bearings in my truck and swithed to Synthetic shell Rotella T 5w-40 weight.
Truck is a little quieter. But now 400 miles later I think the bearings are broken in and now I'm getting all most 20 MPG (a 4mpg increase) in city driving. I don't know if its the new bearings the new oil or both.
Even now sence last fill up, I have driven just about 50 miles and by eye balling the fuel gauge it looks like I have burned about 2 to no more than 3 gallons of fuel. Still some where around 20 mpg.