Mulching creates a dense mat that harbours mold, disease and varmints. I do re mow most of my clippings as they are discharged onto unmown areas. When finished, a few passes with the sweeper and Done. I haul mine to the forest nearby.
You have made a great start in overhauling your engine. You are now overloaded with information. It appears to be a fuel problem. Exhaust glowing red hot indicates a very lean mixture or Cam timing problem. Check all Fuel lines. Blow them out (cap OFF tank) outside as fuel will splash. I...
I suspect the Second from Left Pully has a bent 'axle' . Remove the Pulley, get a piece of 1/2" pipe and carefully straighten the axle bolt. Vertical in all directions.
There is a linkage adjustment near the pedals that can be adjusted for optimum speeds both directions. Speaking about JD X320 and others. Try that Pedal height should be even or the Reverse somewhat higher. Stop mowing steep slopes. You can starve the engine from oil!
I think someone spiked that fuel before or after you got the unit. Check your enemies list and try to get it analyzed. New tank is the best way. Fuel lines too.
I digress. The Planet continues to Evolve as it always has. The Ice Age was only 15,000 years ago. Climate change is real but only a tiny percentage is caused by mankind. WE didn't start it and we Cannot stop it. A volcano emits as much crap in an eruption as we do in a Year. Learn to live...