Why when I drive my 96 ford taurus and come to a complete stop it slip out of gear but when I put the car back in park and then put it back in drive its back moving and shifting normal just only when I come to a complete stop

Have you checked the fluid?

Sounds like it's time to get it to a transmission shop and have it looked over.

The Transmission Range Sensor may be failing internally. For $35 it's worth a shot. Easy to replace.

How-to Remove and Install a Transmission Range Sensor (TRS)

The Neutral Safety Switch is part of the TRS.

REMOVAL:

1. Place gear selector in Neutral.
2. Disconnect negative battery cable.
3. Remove air cleaner and air cleaner outlet tube.
4. Disconnect electrical connector to the TRS.
5. Remove retaining nut (13mm) and control lever from transaxle. Use a large adjustable wrench or suitable wedge, to prevent the control lever (i.e. shaft coming out of the transaxle) from rotating.
6. Remove both TRS mounting bolts (8mm).
7. Remove TRS.


INSTALLATION:

1. Clean and lubricate the shaft coming out of the transaxle.
2. Align the Neutral alignment marks on TRS, using a pair of needle nose pliers. This accomplishes the same thing that the Alignment Tool T92P-70010-AH does; i.e. lining up the two slots on the TRS wheel with the “V” index mark on the edge of the TRS.
3. Install the TRS, ensuring it is fully seated on the shaft, and loosely install both mounting bolts.
4. Verify alignment.
3. Tighten TRS mounting bolts 9-12 Nm (80-106 inch-lbs.) and remove tool, if used.
4. Connect electrical connector to TRS.
5. Install control lever--tighten retaining nut 11-16 Nm (98-141 inch-lbs.). Use a large adjustable wrench, to prevent the control lever from rotating.
6. Install air cleaner outlet tube and air cleaner.
7. Connect negative battery cable.
8. Check for proper operation with parking brake control engaged. The engine should start only in Park or Neutral.