Engine/Transmission (1998.5 - 2002) Surging Idle?

[KenHokie]

I was wondering if anyone has experienced this problem. Truck has 41K miles on it. The truck recently has begun to surge at idle only after it has either sat all night or all day. The funny thing is I hear and feel the surging, maybe 50 rpm, but the tach is rock steady. Once I drive a few miles, it stops. It is only happening at idle, power is fine and constant while driving. The other thing that I have noticed lately is that the fuel pressure (at the input to the vp44) is down 1 - 2 psi from previous. It used to be 13psi at idle, now it is 11 - 12 psi. Maybe the fuel filter is getting dirty??? I have about 6K miles on this filter so it needs changing anyway. I'll pick up a new element today at lunch and change it tonight. Any advice would be appreciated... . tx