1998 Ford F-150 Rough Idle and hard starting

Sir, I have a 4.2 v6 that has 300K miles on it. It reciently ( 1 month) started to develop a rough idle after sitting at a light in drive for about 30 to 60 seconds which forces me to put it in neutral to keep it running. When the signal changes I put it in drive and it sometime stalls when I accelerate. It has in the past week started to begin to crank longer than usual to start. All this is after it has warmed up. The cold start is still normal.

Thank You

Marv Parish
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updated 12/19/08

Thanks for your help.

I added a bottle of 44K to clean the injectors.
However, when I tried to restart my truck last night it would not start.
I changed the plugs. I tried ether and it wanted to start.
I then checked the schrader (fuel pressure port) with the engine cranking and NO fuel leaked out. Do you think the fuel pump is bad or the filter clogged.