In my 2004 Tahoe both my coolant in my oil are disappearing. I have no trace of liquid underneath the vehicle when parked. However, every month or so we will get an engine coolant hot message and I will almost have to fill the coolant with an entire bottle. Same with the oil. But now it's every few weeks it will say the oil pressure is low and I can put in a lot of oil like 2 quarts.
About 150,000 miles on engine. Also have codes p0171 and p0174.