I'm looking for some advice on where to start my diagnosis. I've got a '96 425 with 778 hours on it. I've been having some issues with it sputtering and dying, seemingly randomly. Sometimes it happens under load at higher throttle, and sometimes it will be sitting idle. Yesterday it was running...

Backhoe has sat for 7 years and I have been slowly rebuilding some stuff on this machine and have had the main bearings recently replaced as well as valve lash done by a machinist. That got the engine going and it sounds great. Have been starting it to flush fluids and after about 10-20 minutes...