Post below on filters got me thinking.    I take my truck to one of those Jiffy Lubes.  They tell me they recommend oil changes every 3,000 miles.  My op. manual says 7,500mi interval.   If they're using the cheapest filters and oil they can find is that why they're recommending sooner oil changes?   I always figured they were trying to increase sales but now wondering.   What do you guys think?