After catching wind of the oversize filters available for small/big block Chevys recently, I was curious to try one on my '85 GMC C3500. Since about 2009? I'd been running Schaeffer's 7000 15w40 on a 3,500 mile OCI, switching to 10w30 last time around and being really surprised how obvious the viscosity change was, in a good way. Now, especially after consulting the owner's manual, I thinking I'm going to lean toward a 5,000 mile OCI w/the big filters (Napa 1794, specifically) changed every 2,500. Most of the truck's miles are in 10-40 mile spurts, occasionally racking up 200 in a day with occasional heavy towing. Consumption is around 800-1,200 miles per quart (mostly attributed to old valve seals and leaky oil cooler lines) and there's 121,500 on the clock. Cost difference is something like .23 cents/mile more for the 5K+big filter regimen, but miles per quart (not counting consumption between changes) is within 10 miles difference. Any input yay or nay on the two schedules?