lesabre misfire.

Good Morning, I am sort of at a crossroads here, I had some charging trouble with my 98 which has since been remedied. But in the midst of the charging issues, I noticed my transmission wouldn't downshift if I leaned into the throttle a little bit like it usually would. Instead the engine lugs...

Rat droppings found on engine, 05 LeSabre started sputtering and vibrating while driving then it stalled. Most likely engine is misfiring (unsure which cylinder because I don't have my scan tool on me atm) since the CEL was blinking. Engine turns over fine, but won't stay running. Also noticed...

My 03 Lesabre just started missing on 3and6 cylinders. I checked the codes and it showed a P0300, cylinder misfire. I checked the coil pack and no fire to plugs, so I replaced that coil pack, but I still have no fire to 3/6 cylinders. I even swapped coil packs and still none on 3/6. Any ideas...