I put a guage on it, and key on eng off was getting 10psi.... then I reset it and tried it again and got 40psi... then I reset it and got 10psi... then I reset it and tried again and got 35psi... I checked the fuel pressure because I am having intermittent idling stalls and idle rocking like its choking out... sometimes it goes dead when the rough idle starts... any advice?

its a 1997 ranger 4.0 V6

 

Spec is 45psi for 1997(1998+ were 65psi), engine off maybe down to 30psi but holds steady.

Does the 10 or 35psi hold steady, with key off?

If so then I would say time for a new Fuel pump.

On the Fuel rail is the Fuel Pressure regulator(FPR), it is Vacuum operated, if it was leaking fuel pressure would drop to 0
If a fuel injector was leaking it would drop to 0

On the fuel pump is a check valve, if it was leaking it would drop to 0
Check valve is part of the pump in any case.

The fuel pump should come on for 2 seconds each time the key is turned on, so I assume this is what you mean by "reset it"?

If not turn key on(count to 3) and off 3 times, then test pressure, see if it is stable or dropping

 

it was stable but would sometimes be only 10psi, and other times it would be 40, or 35psi... the manual said bad fuel pump... but I am wondering why do I get a steady 30psi when Idling? could I have a bad fuel pump and it still hold steady at spec 30psi while idling? the truck runs great while going down the road, or otherwise pushing the accelerator.. it is when idling either in drive or park where it gets bad stalling and rough idle... it will get so bad it simply dies...