[Jfrahm]

If it's struggling to turn over even when jumped with a good battery and good cables look for something like a seized alternator or AC or PS, or some other drag. Camshaft maybe.

I suppose the starter could get weak (very uncommon though) but that would not explain the running problems you also observed.

Try turning the engine with a socket wrench, it should be pretty easy to turn but for some bumps when you hit compression and you should be able to let the compression bleed off as you slowly turn past these spots.