Hi there, I am new to the site and am learning what it takes to learn and work on larger for me midsize equipment. I recently purchased a 2006 NH TZ24DA w/ a 24hp yanmar diesel. runs great but just recently when throttling up to 540 to engage the mower blades roughly 15 minutes into cutting I begin to loose RPM's and the it will throttle back up and then back down again. This continues until I disengage the mower deck. The tractor does not do this when I am just using with out mowing but I also do not have the RPM up that high either. Any suggestions and/or advice would be greatly appreciated.