I have the 99 Ram van with a 5.9 it starts up and runs but then dies when it gets warm ....any suggestions

 

I'm curious if it idles rough when it dies. Does it start up after dying or do you have to wait a while til it cools down? Any codes or check engine light on? When was the last tune up (dist. cap,rotor,plugs,wires) Ever clean the throttle body and IAC? what have you done so far? Search out some of the threads on this site for what symptoms yours is having.

I've read through some similar threads to your problem and looks like there's a hand full or both of things that could cause your problem or similar to your short description. Trying some cheap and easy tests to rule some things out first would be easier on your wallet.
A couple are this, Check for codes first, if none then try swapping the auto shut down relay with one of the other same type relays in the pdc box by the battery. Some guys have advised unplugging the forward 02 sensor harness, see if it runs after reaching warmed up temp...

I had a crank no-start last week on my 99. parked it after work one evening having run well all day, but next morning no start. Ended up weak spark from the ignition coil caused it.New coil and all was well again.

 

I havent checked any of those things but will do everything you mentioned ill let you know what the out come is

 

It doesnt idle rough at all, in fact it runs quite smooth

 

Find out what's missing when it dies. Spark, or fuel.