Your machine has a 15 AMP charging system, so at high speed, you should have sufficient current. Headlights & fuel solenoid will use around 5-6 AMPs and PTO probably around 3-4? HOWEVER- IF the battery is low in charge, it may "suck" a higher than normal amount and thus drop the voltage to the point that the PTO disengages. I would start off by fully charging the battery and see if that resolves the problem (at least temporarily). IF the battery is 2 or more years old, I'd definitely get it load tested. As a matter of course, you should ensure that the connections to the PTO SWITCH and PTO are good. You should unplug/plug a couple times to "wipe off" any "crud".

***"I was able to push it into the garage"*** Did you have to select neutral in order to manually push the tractor to the garage? Or....can you push the tractor no matter what gear you select? It is important to know this because: If you can push the tractor manually no matter what gear the transaxle in in, there is likely some serious damage inside the trans. But, if you must select neutral position in order to push the tractor, the trouble is likely not inside the trans at all, but with one of the idler pulleys in the ground drive belt set up. The detail of "burning odor" is significant here because it implies that the drive belt is burning in the engine pulley groove due to another pulley being locked up. At least we hope that is what's going on. If the answer to the pushmobile question is "Neutral only", you will need to do a "hand on" check of both idler pulleys to see if one is seized (if so my bet is on it being the v-grooved idler pulley). Please post your answer and we will proceed from there.

I can't imagine a left turn leaning the mower over so far as to affect the carb. I'm still thinking intermittent wiring. Try- wiggling the PTO knob during both "flat" and the problematic" mowing to see if something "different happens. Check the plug on the Operator Presence Relay for tightness. The relay looks like this- It'll have terminals marked 30, 85, 86, 87 & 87A. The GREEN wire to terminal 85 is the suspect one. It goes from the ignition switch, "through" the seat switch and to the relay. Also make sure the black wire(s) from 30 & 86 have a good ground. That relay is known as a "Bosch" relay and is very common. Car Stereo stores use it for high powered AMPS. Also High/low beam switching on head lights. It's about a $4 part at an auto parts store and $16 at a "tractor" store. Also, recheck your "jumper" on the seat switch.

***"I doubt a "defective air filter" is the cause of a wasted cam lobe on your machine. #2) I doubt the air filter has caused *only one* of your cylinders to give up the ghost either."*** I agree with that. When the air filtration is not keeping dust and grit out of the engine, the first components to suffer are the intake valves and piston & rings/cylinder walls. Secondary components to fail would be camshaft lobes, crankshaft rod journals and piston wrist pins. If you don't "see" any visible signs of filter leakage (obvious "dust tracks" or "dust streaks" showing in the areas "past the filter", dirt in the carb throat and intake manifold (some traces of "carbon black" in the intake is OK. Dirt, grit or "sludge" is not OK), about the only way to confirm the presence of inadequate filtration, is by doing "autopsy" to the disassembled engine and components. In an "autopsy", all engine components are measured with precision instruments (micrometers, dial indicators, "plastigage" to name some)and compared to the OEM specifications and/or wear limits. The two "most telling" things to measure when you suspect that air filtration has been "compromised" or "corrupted", are the diameter of the piston "skirt", and the diameter and taper of the cylinder walls. In measuring a piston, you DO NOT measure diameter anywhere in the piston ring area. The measurements are taken across the "skirt". The "skirt" of the piston is the "long, round surface of the piston sides". The skirt is the portion of a piston that actually "supports", or "carries" the side loading of the piston that occurs when the rod journals of the crankshaft are "half way between TDC & BDC" of piston travel. For this reason, the cylinder walls will wear where the skirt "rides" more than other areas. In most engines, you will be able to actually see the "track" where the piston skirt "touches" the cylinder walls. This track is where you want to measure the cylinder to determine how much it has worn. Measure the cylinder walls that are "perpendicular" to the skirt track AT THE BOTTOM OF THE CYLINDER. This point of the cylinder will give the original diameter of the cylinder when the piston was "put into service". Knowing the "new" measurement allows you to subtract that value from the measurement taken in the skirt track of the cylinder. The "remainder" from that computaion represents the amount of wear that has occurred to the cylinder. In measuring a piston, you take the diameter spec for a new piston and subtract the measurement from the worn piston. The remainder from that computation represents the amount of wear that has occurred to the piston. You can then compare all your measurement results to see if the engine would require "over boring" the cylinder to the next appropriate "oversize" of piston. Over boring a cylinder requires an oversize piston. And, you can't use an oversize piston unless you also over bore the cylinder (they only go as a "pair") If the engine features "cast iron" liners, and dirt and grit are getting into the engine, the wear to the cylinder walls will be worse than the wear to the piston. This is because the "softer" aluminum of the piston allows some of the grit to "embed" in it. The embedded grit acts like "emery" and will cut into the cast iron while the piston itself gets "less wear". Aluminum cylinders & pistons will wear about equally. Anyhow, if the cylinder walls and piston skirt exhibit "excessive wear", the wear is most likely due to bad air filtration. So, if you think you might want to "save" this engine by replacing the camshaft (which is obviously worn), you need to perform (or have it done by a "machine shop") an autopsy to determine if the engine is a candidate in the first place, and if unfiltered air was the cause. With today's costs of machine shop operations plus the high relative costs of individual replacement parts, you have to decide whether to save that engine, or replace the engine. If all other parts measure within acceptable specs, a replacement camshaft kit is likely a good way to go (even better if you can DIY). If the pistons and cylinders (even one piston and cylinder) are worn beyond the service limits, a complete new engine makes more sense. BTW, the 120 PSI versus 135 PSI on the "good" cylinder probably reflects the worn cam lobe more than the leaking head gasket.