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 don't think you can go wrong with the GT 5000 made by Husqvarna. Kdoug makes a great point about the Husqvarna branded machine, especially noting the fabricated super heavy gage decks. If you really are mowing a lot of grass this might be a big factor to consider. The Husqvarna fabricated mower is the same design as they use on commercial products, really solid. Big heavy mandrels on the blades also. Very impressive machine. And of course the GT 5000 at Sears is its little brother. Good luck.

Does your deck spindles have greaseable zerks? Have you greased them before each mowing? If NOT then there's your problem. Trying not to be scarcastic, but there's some people out there who just put in gas and don't do the proper maintenance each time they mow. I have a 2003 GT5K, but it has a 48" deck with around 170hrs on it and it's still going strong. I use synthetic wheel bearing grease on the spindles as it's a high speed/temperature grease. I also took off the outer spindle pulley protection covers to keep an eye on the grass cutting buildup which has a tendency to buildup around the spindles and burn them out due to the heat buildup. If you do remove the spindle covers, do so at your own safety, as now you have moving parts out in the open to catch on pants or getting your feet tangled in the pulleys while in operation if you forget or slip while getting on/off tractor while deck still engaged. Also a couple times a season(usually beginning and towards the end) I remove deck to scrape out old grass clippings and repaint the underside. This gives me a good chance to check blades,deck belt and hand spin blades to check for binding/grinding and replace/repair anything if needed. Good luck Tim

Though its a good idea to keep the cooling fins clean I doubt that's the problem. You can clean them with compressed air by removing the fan shroud and blowing down from the top, a whole lot quicker then pulling the baffles. You haven't provided enough information for someone (at least not me) to offer much help. What do you mean by the blades slow down and quick turning, how do you know the blades are slowing? Is the engine slowing, does your ground speed decrease too? Is this a manual or hydrostatic model? Assuming the engining is lugging when the blades slow down, what happens when you turn off the electric clutch?