I have a 2003 GMC HD 2500 and a work truck, service body 2004 Chevy HD2500 with Duramax LB7s in them. Not sure of the actual miles on the 2004 but having a start issue after it sits for over 1 minute. We have changed the fuel filter base and hoses eliminating an air in fuel issue. The issue is the same on a hot or cold engine. We are suspecting leaking injectors or a bad lift pump. If you let the glow plugs cool and hit it with ether and get some RPMs it will go on and run fine. Very smooth no smoke and plenty of power. Shut it down and restart within 30 seconds pretty normal. Shut down 45 seconds and crank it will restart but more cranking. Let it sit over 1 minute and it cranks fine and fast but will not start or even hit and no exhaust smoke. There is a test in the manual for vacuum to check the mechanical lift pump lines etc. Then a pressure gauge to check high side pressure up to 28,000 PSI.

Is there a tool group available to check these 2 functions on the LB7 engines?