first thing you have to do is find out where the oil is going. at a qt./250mi, I think if it were burning it it would smoke noticeably. I'd drain some coolant out and see if it's in there. I'd also check the air cleaner housing, and check all vaccum lies. you might also want to crawl under the truck with it running, it's possible that its leaking only when it's running, pay special attention to the area around the oil filter adapter.