rough idle bad milage weak jakes

[alexanderjefferson]

i have 2011 prostar with cummins engine oil temp goes from 200F to 225F and the oil pressure drops fro 38psi to 30 psi when down the road and from 20psi to 14psi when idling just replaced bearings the big one and the small one and replaced the oil pump and the oil pressure sensor then meachanic told me i need to replace the oil cooler i just wanna know if his opinion is right because i put a lot mony tell now and also i replaced the turbo and actuator. any advice with this matter will help
thank you