Haven't used it hard in a while, but tried to put it to doing real work and it wants to bog down and die when you push it into a gravel pile. Background: 1990 543 with the Kubota Diesel 1340 hours Air filters and fuel filter changed since the problem showed itself. No indication they had any issues. Tank pickup was removed to replace broken hose a couple of years ago. Strainer was clean at that time. Engine starts very easily. I usually follow the glow plug procedure in the operators manual, but have inadvertently cranked it over when it was 35 degrees out and it started easily. Starts first time, every time (except when I forget to turn the fuel on.). Engine runs well otherwise at all angles and ground speeds. Controls are responsive and equal. Engine will immediately restart easily after stalling and may have just a hair more power for a few seconds after restarting. If you used it to load mulch, you'd never notice you had a problem. Hope I've given all the information you need. I appreciate any help.