i have a 66 duramax diesel and it is having problems starting on 2008 Chevrolet Silverado 3500 HD

it is hard to start or wont start it is also excessively cranking over do you have any suggestions on what it could be

Scanner! Get the truck scanned for codes.
1 more answer
ck fuel filter and repl if not done so recently be careful to get a good seal or you will suck air.also they are great for air leaks at fuel filter drain.(its plastic)