Q: Stalling misfiring CEL

My 4.0L TJ Sahara had 300,000 miles on it. I hopped in to start it, and it cranked but it wouldn’t start. The Check Engine Light with codes P0340, 0135 & 1391 came on the dashboard. I replaced CKS and CPS w/ OEM but not the oil pump drive assy. After replacing those parts it started right up – then went right back to cranking with no start. No Check Engine Light or codes came up this time. I replaced the sparkplugs OEM, checked fuel pressure and did spark test. I tried to start my jeep but got a crank w/no start. Then I took it to the mechanic and the oil pump drive assy was bad which ruined the new CPS, so he replaced the assembly and installed another CPS. So I drove 30 miles home and it stalled in my driveway. The Check Engine Light came on again with code P1391. It started up right away but idled rough and stalled when rpms got low. Then the codes 0351, 0352, and 1391 came up. I installed a new coil rail and it fixed 0351 and 0352, but I still get 1391 code. The mechanic says it’s still misfiring at 2500 – 3000 rpms. The catalytic converter was shot, needs new 02 sensors and issues with the timing componenets.

I want to replace these myself, so should I replace the 20 sensors before replacing the catalytic converter? Would a bad catalytic converter ruin my 02 sensors? They are still the original ones. The components are 300,000 miles old. Couldn’t I just replace them instead of getting them tested? It is so far away where I have to get tests done. To do this I have to remove the radiator, water pump, timing chain cover, remove the gear from cam shaft and the chain; install new gear or gears and chain then put everything back in. Would that be too hard for me? Or should I let the mechanic do this? The mechanic thinks the 1391 code is probably from timing components, cats or 02 sensors which is leading to the misfiring and higher RPMs. What do you think?