I was leaning towards broken parts in cat or (and this may still be) a wiring fault on o2 sensor but the key is your speedo jumping when prob happens. that makes me think electrical. check batt terms take off clean dont just yank, check grounds. I assume your batt is straped down so cant short in turns? check o2 sensor for bad wires or conn may not code.oh and when you say wouldnt start on hill i would park on hill get it to not start and see whats not there like spark or fuel