I went a short road trip this weekend and while going up a hill under load the car started to buck a little bit. Shortly after it completely lost acceleration altogether. I pulled over let it idle for a moment and took off no prolems. It hasnt lost power since then but it still feels like hitting bumps when under heavy loads. I would guess its not a clutch issue since it still pulls 10+ PSI. The CEL has been on since I bought the car and up until this weekend it had no issues. My first thoughts are spark plugs, fuel filter, or air filter. Since I just bought the car used I would guess these all need replacement. Im not sure what grade of fuel was in the car but I filled it with 91 octane. There was less than a gallon in the tank because i didnt want to mix octanes if possible, could 1 gallon of a lesser octane have caused this? It's a '05 SS/SC with 58k mi. Could there be a larger issue?

 

I am dealing with similar issues

 

For the way I understand what Octane is (Fuels ability to resist detonation, and the % of the Octane Hydrocarbon, H18C8 to septane H16C7 I could be wrong but I bleive im failrly close)
Mixing octanes = no big deal, Youll just get an average octane of whats in the tank.
IE: 5 Gallons of 87 + 5 Gallons of 93 = 90 octane.

You mentioned you were climbing a hill and under load,
Ifyou had 1 gallon left, its possible that the gallon was pulled to the back of the tank due to the incline, resulting in fuel starvation. Also, what were your RPM? Gear? Could be elevation issue, or not enough RPMs. If your climbing a steep hill you need higher RPMs for the extra torque.

oh and I just see you said 4500 RPM wich is probably a good climbing RPM.
So Not sure then,

 

by any chance have you checked your check engine light? Assuming that they don't go on for the hell of it.. you have a problem.

 

I had filled up just before the trip so it wasnt because of low fuel. I was in 5th gear bout 3000 RPM, so roughly 70 mph. RPM began to go down and the car bogged so I put it in 4th and instantly the RPMs dropped and bogged, same with 3rd. I didnt have the exact issue after that though. It's just very sluggish at 4500+ and feels bumpy.

 

Check the CEL

 

Don't our cars have a MIL instead of a CEL?
Ok yes, now im being a smartass :p

 

Almost sounds like it's starving for fuel under load so fuel filter or fuel pump would be my first shot.

Get the codes read, they can be a goldmine of info when you are trying to figure out a problem......

 

Fuel issue is the first thing that popped into my head. If the fuel filter is plugged up it might be causing your problem. My father has a truck that was stumbling/dying when at higher rpm and we replaced the fuel filter and it solved the problem. Good Luck!