What causes lose of power when u depress accelarator pedal hard and driving up hill

check the fuel pressure

Need more information. Year, make, model and engine size please.

Sounds like the fuel pressure regulator in your EFI (carburator). Sorenson make a rebuild kit complete with gaskets, screens and regulator for around $30.

Most modern automatic transmissions have a chip in them that will prevent the car from downshifting, say, into first gear when you're moving at 60 mph. Still, I wouldn't try it. When climbing a hill, only downshift if the AT can't decide which gear to be in and switches back and forth--choose the lower one. When descending use brakes to decelerate. However, once you've braked, do use a low gear to coast in, to prevent you from freely accelerating down the hill.
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GM Tech2 GM Diagnostic Scanner With C card

have you looked up the codes? sounds like a clogged filter or bad fuel pump. Either way, have the check engine light looked at.

could be a wiring issue to the tp sensor its self or a problem withe the throttle body or pcm

Check the sock on the fuel pump inside the fuel tank..might be clogged

You may have a fuel issue the cheapest thing to do is a simple fuel filter replacement an old filter can cause backups in the gas line. Also check to make sure your air cleaner assembly is fully hooked up and no hoses or clamps are loose. less air cause these same symptoms.

HAVE SOMEONE CK THROTTLE POSITION SENSOR AND CATALYTIC CONVERTER MAKE SURE EXHAUST IS CLEAR

The hold light is probably for a fault in the HILL HOLDER SYSTEM

This system holds the Forester on a hill without using the brake pedal, as long as you keep the clutch depressed. It's very useful when towing.

I will check my workshop manual as soon as I have some free time and try to get a definitive answer for you.

Regards,
Andy, Derbyshire UK