1993 Subaru Impreza fuel

You need to check 2 things for me. First, you need to confirm that you are getting a good hot spark to the plugs. Next, you need to test for fuel pump pressure at the fuel rail.

One other question. Was the timing belt ever replaced? Does it sound normal when the starter turns the engine trying to start it?

If fuel pressure is good, injectors are getting power, spark is good, timing is good. That doesn't leave too much. Since you were struggling to get up hills, that tells me there was a power loss. Have you checked engine compression? Have you checked to see if the catalytic converter is plugged?