Car starts but won't stay running it's a 99 buick Regal GS Supercharged

no easy fix need to replace it --replacing it is the easy part getting everything out of the way is what is time consuming
03 Regal Gs Intake Gasket Replacement Yahoo Video Search Results

Should be at least 35-45 psi.

What is the problem you are having? Transmissions are complex, especially automatics. So if you are asking this question then, I would recommend taking it to a trusted ASE certified mechanic.

should be on the fuel rail, take the plastic engine cover off and you should see the injector rails on either side of the supercharger, got to be real close to the line towards the firewall

As you see I provided you the models you can apply the transmission :The 4T65E-HD (code MN7) is a heavy duty version of the 4T65-E used with more powerful engines such as the LS4 V8 and L67/L32 supercharged V6. Applications: 2.93:1 MN7 Pontiac Bonneville SSEi L67 Chevrolet Impala L67 Chevrolet Monte Carlo L67 Pontiac Grand Prix GTP/GXP Buick Regal GS Buick Riviera L67 (97-99) So ,yes you can!

The replacement of the forward clutch requires the automatic transmission be removed and rebuilt, Cost about $2500.00

can you give more detail did it start to run rough,how much oil is on the dip stick,does it turn over,????

You have a problem in the fuel pump relay circuit for sure then. I'm betting the relay, but it could be that dropping resistor.

Check the idle air control as it is operating when you start the car and after the car warms up it is out of the system.

It's probably an alternator, or an alternator fuse.