02 nissan sentra lacks power

[suddhad]

I have a 02 nissan sentra gxe with 100k miles. I got it used when it had 70k miles on it. It is very reliable and gives me great milage. However I noticed when I drive uphill the car lacks power and is unable to pick up speed. If I drive too long uphill at high speed the engine starts getting hot and I am forced to slow down.
I am a Automotive Technology student at a Community college and would like to diagnose this problem myself.
I changed the spark plugs recently and that did not slove the problem. I was suspecting it might be the fuel filter. However on a 02 nissan sentra it is in the gas tank and is not replacable.
It can also be the oxygen sensor. However I thought the car engine lights will indicate when it is time to replace the oxygen sensor.

Does any one have any suggestions ? Thanking you in advance.

[dabogdan]

mine does the same thing, especially when the cruise is on. I've got about 130K on mine. Runs fine though. I just don't worry about it.

[mpe235]

Possibly a restricted exhaust. Catalytic converter failure at that mileage is not uncommon.
You may also want to do a compression test and a cylinder leak down test. I have seen head gaskets on these fail between the cylinders and allow compression to escape into other cylinders. This would probably be more noticeable under heavy loads until it gets bad enough and then it would probably run real rough or start extremely hard.