Why was the original engine rebuilt; did the car have a oil sludge problem?
Who did the work; what level of expertise do they have? (e.g. normal shop; specialized vw shop etc.)
When you had the oil pressure tester installed; what was the psi?
When you replaced the coolant temp sensor; what location was it? (There can be more than one)
Did you inspect and test the wiring; from the coolant temp sensor and confirm the plug was in good condition?
Have you gotten any trouble codes; related to the cooling system?
Did you replace the the thermostat and is the cooling system temps correct?
(e.g. the temp in the speedo and what the temps are showing in the live data/scan tool?)
What scan tool are you using?
While the new beetle and Passat have a similar engine; they are different cars. I would be looking at PassatWorld.com or audizine.com for help as well.
As a basis for testing and diagnosing problems; I suggest we start with the service manual here:
2001 Passat Sedan with 1.8T (engine code AUG)
2002 passat 1.8t wagon (engine code AWM)