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...
A 21 or 22" will suit you well. You can often find suitable and reconditioned older mowers for $200 or less. Skip the Mulcher/bagger types.
1/3 acre ( 14,520 square Feet) minus home/garage, laneway, trees etc isn't much to mow. Older 3+HP Briggs and Stratton powered (not the newer Chinese...
Only mow when grass is Tinder Dry. After changing the oil, I remove my Deck in the Fall and turn it upside down on a gravel area and pour the used oil into it, swabbing it on all sides and protruberances. Leave it overnite to soak into rusted areas.