I just purchased a farm a few miles from my currant home in Pa. Im pulling my dump and deckover trailer back and fourth. Im using Delo® 400 XLE Synblend SAE 10W-30. My truck runs great on it and I change my oil every 3,500 miles. Im doing very short runs and pulling pretty heavy loads back and fourth. My question is since I change it every 3,500 miles does it matter to change over to 5w-40? I figured the 10w-30 will hold up fine since Im changing it out at 3,500 miles. I was thinking maybe I should get an oil test done to see how its working.