OK, new question, and I know you folks all want Mrs. Cusser to be happy...
Mrs. Cusser's 2005 GMC Yukon Denali with 6.0 engine, almost 200K miles. She says that for a month or so that on first startup of the day that there's a message stating "oil pressure low" that appears, but the oil pressure light goes out as normal, and the oil pressure is also normal. So she switches the engine off, and starts it again, and the message does not re-appear (until first startup the next day). The oil level is fine, I've used 5W-30 full synthetic for the 8 years we've had it as did the previous owner. There are no other engine issues or noises. Morning low temperatures are about 45F here. Any ideas??? Thanks.