1998 Oldsmobile Intrigue engine/trans

I have a constant clicking sound under the hood and low oil pressure light on.I was told the intake manifold gaskets need to be replaced. Is there anything else I could check for? But I recently was driving and the car slowed down by itself. Went home n parked it now it won't move when I shift into reverse please help.

It's really difficult to identify noises from just a description because there are tons of moving parts that have the potential to create a clicking noise.
If the oil pressure light is coming on first check the engine oil level, If it is good then you need to attach a oil pressure tester to see if the oil pump is creating pressure because if its not pumping engine oil through the engine then sever engine damage will result (no oil pressure will also cause clicking, clacking noises).
These engines have a history of lower intake gaskets leaking coolant into the engine oil or vise versa (or both). Signs is oil or coolant at the lower gasket area or coolant in the engine oil or muddy or milky colors in the coolant.
Have you check the automatic transmission fluid level ( do this check with the engine running and the vehicle on a flat level surface). Make sure the transmission fluid level is good and the fluid condition is red not black or milky in appearance.
Thanks for the question

Coolant pressure tester will pressurize the cooling system and force coolant out of any leak. Most auto parts suppliers have a tool rental program you can get that from.

As for the noise not sure? If it is a loud ticking noise when driving then there is a possibility a exhaust leak. It is usually worst when the engine is cold and the noise will decrease when then engine warms up.

If a lot of plastic fell into the engine oil pan then that could be a possiblity of low oil pressure but unlikely either the oil pressure sensor is plugged up or is not working. If the oil pickup tube is plugged that would also cause a low oil pressure issue or the oil pump has failed. Either one of the two is bad and would cause engine damage.

If you have a check engine light on have it scanned for codes and given them to me because maybe it will give some information about what is going on. If no codes are present and the trans oil level is good then most likely the reverse in the transmission bad.
Bad motor/trans mounts won't cause the transmission not to work just thumping when the engine/trans lifts off the mounts and fall back down.