2002 Nissan Quest

it probably does need a tranny fluid change, but this wouldn't account for loss of power. The tranny is only reacting to the power provided by the engine. I'd think it's starting with power loss from the engine. The easiest and cheapest place to start is the fuel filter. It's probably getting plugged and restricting fuel flow when more power is required - as in going up a hill. The filter is about 8 to 12 dollars. The auto parts store can tell you where it's located.