Have trouble starting GM 3800 after replacing fuel pressure regulator?

During one of the hard to start episodes shoot some fuel or starting fluid into the intake, that will confirm a fuel delivery problem in just a few seconds!

Put the old regulator back on.

A noid light is used to confirm pulse to the fuel injectors.

I had a Pontiac it behaved like this, turned out to be the engine computer.

Go look up some diagnostic procedures for your specific application. Changing parts is going to add up.

What is your fuel pressure?

Try disconnecting the MAF sensor while the motor is turned off. Then try starting the motor with the MAF disconnected.

What's the fuel pressure?

When the motor doesn't want to start is there spark? You also should listen for the injectors to be clicking while cranking the motor over. No spark and no injector pulse is likely a crankshaft sensor problem.

Check the spark plug wires that plug into the coils. I have to clean the rust off of my coil towers every 6 months.

When you did the balancer you probably damaged the crankshaft sensor that should have been replaced at the same time.

The crank sensor is a little tricky, you fold a paper match stick over the balancer vane to center the sensor windows and then fully tighten the sensor mounting bolts, then the balancer. When you start the engine the match stick falls out. If you don't do this the balancer vane will destroy the sensor the instant you attempt to start the engine.

If it only started giving you trouble after the regulator, then you did something wrong at the rail.

Just keep replacing expensive items at random with no idea what you're doing. That always works.

did you ever think it could be the fuel pump causing you all the troubles

Fuel pump maybe, have you checked fuel pressure?