2000 Dodge ram 2500, cummins diesel.  180,000 miles.

Driving along about 35mph yesterday and the engine went dead.  My
first thought was the fuel pump had gone out again, as I had it
replaced about 40,000 miles ago when it did the same thing.  (Last
time it would not restart crank but not fire and they did replace the
pump. )
I  checked the fuse/relay box and found no blown fuses,  pulled and
replugged the Fuel relay, and after a little cranking it started back
up.  So now it will go for a while and dies, it seems that I can pull
that relay in and out a couple times and it will restart.  I swapped
that relay with the fog light relay (same relay) and checked the
wiring in the socket end no problem found.
Sometimes it will die after less than a minute other times it will run
10-15 miles.  If it tries to die at freeway speed,  I can play with
the pedal and it stumbles along for 5-10 seconds and clears up.
Odd because it will do it at 65 mph or at idol at a light.

The engine light is on, but I do not have a reader for the codes.

Thanks for any help!
Paul