Falling fuel pressure

My friend has a 68 dart slant 6.
He said the car was running rough, not idleing as before. So he did a pressure check
on the fuel line between the pump and carb. He said it was barely 1 psi.. So he replaced
the fuel pump and (I was there) the car was started and the pressure was a little over
6psi. but after about 5 minutes at idle it went down to 3psi.. I had noticed all this time
that there was hardly any fuel in the filter (clear plastic) I thought he was picking up
dirt in the tank. Yesterday he tell me he checked the tank and the filter was fine..
he says it's a worn cam ... I don't get how a worn cam can be "good" one minute and
then bad.. Mechanical parts don't usually show that type of symtom, good to bad
and back to good..
Just would like another opinion...
On another subject. I've never heard of or done it myself, but soaking a new timing
chain in oil before installing it. I see no harm, but would not doing this cause the
chain to wear faster.. So this on the "garage squad" the other day...
Best