1995 Other Oldsmobile Models oil gauge

Electrical problem
1995 Other Oldsmobile Models 6 cyl Front Wheel Drive Automatic nueng miles

On 03/08 had new engine put in 95 olds achieva. I have taken the care back under warrenty because my check engine and oil pressure lights keep coming on. And the oil gauge while driving goes from high to close to red zone. The mechanic shop stated that the have replace the sending unit twice. They also state that the gauge cluster needs to be send out because the problem is electrical and that I will have to pay the mechanic in there shop and what ever the gauge tech company charges to repair it.I dont know if its a vacume hose or what but I need help please. Thanks for your presouis time.