1998 Grand Prix GT - PO107 & PO108 Codes, White Smoke, Coolant Loss After Intake Replacement

I own a 1998 Grand Prix GT and recently encountered a persistent issue after replacing the radiator due to a cracked component. The car overheated one day, and I stopped it immediately to let it cool down. After installing a new radiator, I began noticing coolant loss at approximately one gallon per day. Two days later, I observed water in the oil, which led me to suspect a blown head gasket. However, compression testing showed consistent readings of around 120 psi across all cylinders. Further research revealed common problems with the upper intake manifold and intake gaskets on this engine model. As a result, I replaced both the upper and lower intake manifolds along with their associated gaskets. Upon disassembly, I found that the lower intake gaskets were blown at three locations. The engine was then reassembled, and I also replaced the oil, spark plugs, ignition wires, and valve cover gaskets. After starting the car, the check engine light activated but went off the next day. On the following day, it came back on, accompanied by rough idling and noticeable sputtering during acceleration. A small amount of white smoke is now visible from the exhaust pipe. The vehicle is now displaying Diagnostic Trouble Codes P0107 and P0108. Importantly, these symptoms did not appear before the engine was disassembled — they only emerged after the intake work. I've already spent more than I can afford on repairs and am considering abandoning the car altogether. Can anyone provide guidance on what might be causing this? The issue seems to stem from either a faulty manifold absolute pressure (MAP) sensor or another component related to the 380 or 3.4L engine system.