NO POWER EXCELORATED - 1996 Nissan Quest

Will not move at all or very slow responding ? Fuel pressure issues and fuel injection issues are possible . Clogged exhaust , restricted intake , any number of sensors or their wiring/connections to the engine module .

put engine flush in it first till oil hot then drain it,change the oil filter.and refill with 20/40 oil.

Are your catalic convertors on the exaust plugged up?

Here you haven't mention your model name, Go to the given link which is online store known as reliable, they have repair manuals, I am sure you will get the solution Best Manuals

Find out what the codes are for and replace faulty sensors

maybe a plugged transmission cooler.

any warning lights on?

you could need a tune-up(plugs,wires,fuel filter,air filter)or you may have a bad ignition coil causing misfire.this is where you need to start.

check egr or your mafs ok

Issue with the trasmission needs to be addressed.