Losing power going uphill signals the possibility of worn piston rings or exhaust valves. Worn out rings or valves may signal low compression problems with the engine.
Without a tight seal on rings and valves, a car leaks pressure and its engine doesn't work efficiently. The first step is a compression test. A mechanic manually tests the engine using a compression gauge or by using a computerized engine analyzer. The compression test checks each cylinder and determines if pressure loss is at the piston rings or the cylinder valves. High compression readings usually indicate problems with the rings. No change in compression readings may mean bad valves.