Rattling noise 2001 4x4 Blazer has a rattling noise and not much power especially up steep hills, runs great other wise. The sound is there even when in park. and doesnt seem to get any louder when driving, though I can not hear it over the sound of the engine and road noise.

SOURCE: loses power on steep grade

Sounds like you need a clutch replacement.

Try this. Go somplace where there are no cars, and no possibility of running into anything. Stop the car. Set the park brake. With the engine running, put the vehicle in 1st gear. Hold the foot brake pedal, and give it gas, and let out the clutch slowly.
If the engine does not stall real quick, the clutch disc is bad.

SOURCE: parked on steep hill have to give a lot of gas

Are you driving an automatic? It sounds like the clutch plates inside your transmission may be slipping. Yes, automatics have small clutch plates between each gear whereas a standard has one big clutch plate

SOURCE: Vehicle overhetas on a steep incline

MIne did the same thing it overheated going up in the slighest hill or pulling the littlest of trailers i replaced the radator and now i can go up any hill or pull anything without it overheating,first i changed the thermostat and sensor then clutch fan i even put a aux fan in in ,none of that helped after i changed radiator it did the trick hope this helps my truck was a 95 f350 with a 7.5 460 in it

SOURCE: why is my 1993 jeep grand cherokee slipping out of

the transmission cable needs to be adjusted on the side of transmission