My 2007 Tacoma 4.0L is approaching 83k miles. For most of its life, I've used Toyota 5W-30 from my local dealer. They quit carrying it a couple years ago so I switched to Pennzoil High Mileage 5W-30. My truck only sees 5000 miles or so a year, bit it's almost always towing miles (3000 - 3600 lbs normally, well within the 6500 lb limit). I've been thinking about switching over to Pennzoil Synthetic. Is this a wise move with 83k miles already on the truck?