1998 Pontiac Grand Prix shuts down in Drive or Reverse

This is can be a faulty reverse gear activation switch and can be confirmed if the lines to the reverse switch is removed or if the fault goes off when you are changing few times from the reverse to the first gear. If not check for short in the wiring harness or in the rear light assembly circuit.
You can disconnect the rear assembly and take a voltage check.

the fog light bulb in the 98 Grand Prix is easy pull pigtail off light turn light from back and it will come out , replace is reverse obviously , but make sure the orientation is correct on housing as there is one tab bigger than the other 2 have to look at it from underneath to see orientation of the bulb housing.

Your transmission for the GTP should be the 4T65-HD. If in fact it is not then that could very well be the problem. The 4T65-E is for the other 3.8L naturally aspirated models.

the transmission has failed, the fact that u still have reverse seals the deal, it is the classic symptom.

Sounds like the filter might be plugging up. I would have it serviced. Do you have a check engine light on? How long do you have to leave the engine off before it will start moving again?

if it only knocks or clunks puting in gear or gettingonit I would check motor & trans mount both upper dog bone & cross bars to core support

torque converter clutch is bad unplug square plug on front side of trans it will work fine without it

my 1998 grand prix does the exact same thing. It just shuts off while driving. I still have battery power. I have called pontiac dealers in my area and they dont seem to have any idea to fixing without changing everything in hopes the hit the problem
Can you narrow it down.

Remove the center console.
There will be a bulb underneath the PRNDL(Park, Reverse, Neutral, Drive, Low) - quarter turn to the left. Pull bulb down; put new bulb in - put back in hole quarter turn to right - reinstall center console...

2\3 solenoid stuck on. Direct clutch malfunction.