trouble starting

I have a 1994 GMC truck it will not start when it is hot .. but if you let it set for awhile it will start fine can anyone help????::confused:

my stepfather also has this same problem for his 93 gmc 3500 with a stock 6.5l diesel, he has been told its poor batteries but no avail. he has replaced the controller twice at $100 a pop also to no avail. I know this sounds crazy being its a diesel but it acts alot like vapor lock. (similar aspects i.e. starts cold but dont sound like it gets enough fuel to cumbust and fire).

any help we can get on this is greatly appreiciated and NEEDED...lol

thanks
Chad

Check the fuel system for small air leaks that can let air in as the fuel tank cools from being over the catlyic converter.