So I have a 96 Tacoma 4x4 4cyl delivery truck with 80,000 miles with a metal frame work in the back. I have no doubt my employees drive the piss out of it. We use it to haul pretty heavy loads 2x a week about 250 miles...it has a helper leafs in the back. Otherwise it just runs around town in city traffic. How often should I change the oil and filter 3,500 miles or can I go longer?