Hello! I'm Rixster...
I'm going to help you out on this but I need some info first...
How many Miles on this vehicle?
How Long has this been going on?
I think I would have the exhaust system checked. You may have a plugged or partially restricted exhaust. This problem would be more prevalent under a load such as your hill climb.
You should be able to take it to any reputable exhaust shop for this check.
They should be able to make recommendations from there.
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There is a big difference!
Under load you are using more throttle hence pushing more air thru your engine.
If there is a defect in a muffler or catalytic converter it can cause your "lack of power" problem and make the engine heat up hence causing your valvetrain noises.
What were the DTC's that were set? (you said you had a check engine light come on)
DTC is Diagnostic Trouble Code.
And No It may not do it all the time that's why I said a possible "defect in a muffler or catalytic converter". If the converter is degraded or broken up on the inside you may not see it effects until it re-positions itself like when you are going up a hill.
The Muffler shop should test this for free.
You can also tell if you hit the converter gently with a mallet and it makes a "rattle" noise it's bad. But as I stated it "COULD" be these things.
Do you know what codes were tripped???
I understand that for sure.
Have the codes checked and we'll pick it up from there. Is that Cool with you?
I HAD THE CODE CHECKED AND IT WAS CYLINDER ONE MISFIRE.