Those codes are common. There are a number of reasons why P0088, high rail pressure, can set. It often sets in tandem with P0087, low rail pressure.
P0045, VNT failure, unfortunately usually ends with turbo replacement. If there is power, a good ground, and CAN at the VNT controller connector, and the code still sets, it's gonna need a turbo. The VNT controller is not available separately, it's calibrated to the turbo.
If you end up putting a turbo on it in the future, now is the time to address a possible problem. The exhaust manifold studs love to break on these engines, and I wouldn't be surprised if the ones in the back are broken. There is a TSB on updated studs and spacers to fix this issue. The exhaust manifold will likely need to be milled or replaced if this condition exists.