cfowinkle

I have a 2008 GMC Sierra SLT 1500 Z71 4X4 (GMT902) Engine: (LC9) 5.3 Liter Vortex Flex Fuel V8 SFI Transmission: 4L60-E I bought it January 03, 2015 with 86,204 miles, the day I drove it off the lot I recieved a LOW OiL Pressure warning "SHUT OFF ENGINE". I pulled over and called the dealer. They asked me to confirm that it had oil in the engine, which it did and to bring it back. Once back, the service department looked at the engine and said that they need to install a Bosch oil filter instead of a generic one. So they did another oil (Castrol Oil) & filter change and the problem went away. Fast forward to March 13, 2015 two and a half months and about 4,000 miles later. I notice that the oil pressure guage start acting strange, it would drop to no pressure on braking and would move up to 60 PSI on acceleraltion. I checked the oil and there was no oil on the dip stick. It took 3 quarts to get it a little more than half way up the dip stick. After this iInoticed the the oil pressure sensor would move up near 60 PSI when I would give the engine gas. So on March 16, 2015 I took it to the local Chervrolet Dealership. They looked at the engine and stated that it needed a new engine, cost $8,000.00. I then took it back to the dealership I purchased the vehicle from because it came with a 100,000 mile Limited Powetrain Warranty. They call it their CCP (Certified Confidance Protection) Plan and advertise it on all their used vehicles. The Dealer that I purchase from is a Porsche, VW, Volvo dealership and does not want to work on the engine and wanted to sub out the repair to Cheverlot, (which sound right to me). The Warranty company is CNA and they stated that if there is not a broken/failed part they would not replace the engine and that the problem my engine has is most likely a a wear item, like built-up carbon on the pistons and rings. They also said I would have to foot the bill if the the Chevrolt dealer pulled the engine and no actual failed item was found, at a cost of $1560.00. The Chevrolt Dealer agreed that it could indeed be that but that the engine needs to be replaced. I have gone back and found that this engine was worked on under warranty by the previos owner at around 33,000 and then again at 66,000 for the oil consumption but it seems that it was never correctly fixed. First the valve cover was replaced and then something else to do with lifters. If they did not correctly fix the vehicle the first time or the second time for the same problem, shouldn't they be required to fix it under warranty? I am totally fusturated. What can I do?