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While #1,and#2 eng running utility sys press,  Brake press, and rudder booster pressure is 2800 psi but when the control stick moves extreme forward perss drops to 2000 psi and remain same but when control stick puts back it is normal.....when elevator booster shutoff switch puts off the press indicated normal....no hydraulic leakage found from the system.

we alrady cleaned and replace the hyd filters.

please give me some suggestions on this regurd....

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NO defect

There is an internal bypass for the elevator; when full forward it can drop pressure below the minimum 2900. IF your pressure is "Normal" (which you say it is) with the control stick pulled off the forward stop your aircraft is OK and there is no reason to worry. The boost shutoff confirms the operation of the bypass. There should be some discussion on this condition in the flight manual.  

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2,000 is too low.  

When doing this check, make sure the engines are at NOT in LOW speed ground idle (hydraulic system pressure MUST be checked with engines at normal RPM.)

You should have normal system pressure (above 2,900) with the elevator pulled off the stops (mid travel, elevator surface streamlined)

Once you put the elevator back on the stops, you will see a drop in pressure (usually no lower than 2,600).

If you have 2,000 PSI when your control yoke is full forward (on the stops) and nothing else is moving in the hydraulic system, you have a bad elevator boost pack manifold that will only get worse the more you operate it.  

IF, you have 2,000 PSI with yoke forward (on the stops), AND engines are in HIGH speed.  You most likely have a bad boost pack.  BUT, this condition can also be caused by a weak engine pump, bypassing pressure relief valve or other failed components (most likely the pack or pump).

I am assuming you have an older C-130 (B/E or maybe an H).   So you most likely have the manifold with a 2.0 GPM bypass in the elevator.  

This 2.0 GPM bypass will be amplified when your engines are in LOW speed because your engine pumps are not putting out the rated 8.6 GPM per pump.  

An easy was to isolate the pumps would be to run both #1 and #2 at HIGH speed (not LOW speed).  Leave the elevator on the stops and turn off one engine pump at a time.  See which one makes the system pressure drop the most.  If you have a failing pump, it will be obvious.

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