So, I'm kind of new to all of this. I just recently bought a 04 Silverado. The guy I bought it from said he was having low oil pressure problems. He said he replaced the oil pump, and it didn't fix the problem. He then said he replaced the engine to a 07 vortec. I have had the truck about a month and all a sudden it is telling me low oil pressure. I'm assuming with my oil pump is bad or need a new sending unit. The guy did give me a receipt for the engine he apparently put in it. Though didn't have a receipt from the shop actually putting it in this particular truck. So, I'm starting to wonder if he actually replaced it. Can someone tell me where to find the VIN of the engine so I can try to match it to receipt?