my old pete 379 had a 3406C , and another had a 3406E. . the E model would never over temp, even when I tried to lug it, it would never go over 700-800°f post turbo. cruising down the highway at 80-95 MPH, it would run about 400-500°. . around 70 it would run about 600°. I am surprised that your cow truck has a speedo. Petercar makes a "Cow Taxi Package"... Where there is a big clock in place of the speedometer, 13 or 18 speed, either with 2 overdrive gears, and 3. 08 rears! haha! Aint no feelin' like Cow-mobilin! Whoop Whoop!
-Chris-