I have an aftermarket warranty on my 2001 F-150. I want to follow the maintenance schedule so when I do get repairs done, the warranty company can't deny me for any reason. Th 2001 owner's manual online says that the truck gets maintained every 5,000 miles (mainly oil changes). Why does the dealer always send me cards saying my maintenance is due at intervals that contradict the owner's manual. Like every 3,000 miles. Is this just so they can make more money off me by having more oil changes?

Which one should I follow?

Thanks!!!!!