What causes sudden loss of power when going uphill?

being very low on gas will allow the inlet to the fuel pump come out of the gas when going uphill. just add more gas and try to start it for a bit to get the gas going again

When you require full power from your engine, weak spots will show themselves. Ignition must perform at maximum voltage, any carbon build up in the dist cap or rotor, Age cracked plug wires or old spark plugs and the ignition system cannot answer the call. Any of these type of issues feels like something is turning off and on very quickly not allowing the engine to increase in RPM.

Same holds true for fuel delivery. Being low on fuel just means your low on fuel. The pickup tube or what ever vehicle specific application is used is always mounted or access's the lowest point of the fuel tank. Some have filters built in to the pump and some use in-line filters. You usually are unaware of a fuel filter starting to plug up with dirt during normal driving. You might notice it on the highway if your trying to pass a slower car and yours does not have its normal punch. When pulling hills your asking for 100% performance from your fuel system and a partially plugged fuel filter cannot deliver 100%. Depending on how plugged up it is will determine the % of fuel delivered to the motor. This issue is smooth operating of the engine, no jerking or stumbling, just flat out does not make any power.

If your a sane driver, neither of these issues will affect you except when going up hills. If your an insane driver, you noticed these issues a long time before you started climbing hills.