My first post here, I've read lots of useful info but cannot find anything on the problem I am having. Motor is a Kohler CV730, 25hp in a Sears tractor. About 250 hours on it, all maintenance up to date. Recently replaced a head gasket, but the problem I am about to describe was the same before and after I did the head gasket. Problem is I loose power/RPMs under load going uphill. Even slight grades are an issue. Steeper grades take me to the point of stalling unless I slow to a crawl. The same grades are not an issue if the deck is disengaged, so without that extra load there is no problem. There are no obvious external signs from the motor, no backfiring, no missing, no smoke. It just progressively slows until I remove some load by going really slow or disengaging the deck. The problem clears within a few seconds when I return to level or turn downhill or disengage the deck. I dropped the deck, cleaned, and inspected all of the bearings and belts. Everything is fine, no loose bearings, all spin smoothly by hand. I think this rules out excessive load from the deck components. Next thought was fuel starvation so I pulled the carb, float level matches spec, and everything is clean. Fuel system is clean all the way from tank to carb and fuel filter is new. I swapped the fuel pump from a working tractor but this made no difference. Air filter is new as well. The choke, throttle, and governor mechanisms appear to be working correctly. Plugs look fine, dark grey but no oil or soot, I'm not thinking they are indicating overly lean or rich. Battery is healthy with a full charge. I'm going to make a leakdown tester next to see if there is a valve or ring issue, but I really do not expect anything here with only 250 hours on it. When I had the one head off to replace the gasket the cylinder and valves looked pristine. Has anyone experienced something like this? Any troubleshooting tips?