I am kinda reading between the lines on your problem , and one thing I'd say you are doing wrong is you keep referring to "the mechanic checked it out and it's ok ", if it's still not fixed I would take anything for granted ----- the thing that gets me is you say you have to rev up the engine to get it to move and it shuts down on the same amount of running time , sounds like the pressure is low at and idle , it may be as simple as a loose drive belt , if the belt breaks or is so loose that it doesn't turn the pump properly , the unit will shut down after about 30 seconds to a minute from a no or low hydraulic oil pressure reading , the sensor that sends that signal is the one on the right side of the hyd filter head , there is a little fitting in between the sensor and the fitting off the side of the head it is called a snubber , it was that porious rock material in it like on the old style fuel filters on carbs of chevy trucks , it will sometimes get some trash in it and block the oil from getting to the sensor , some 7 series units when you change that hydraulic oil pressure sensor they will give you one that is a little different and you have to get a wiring pig tail to make the connection to the new sensor ,-----there is a silver connector under the cab right close to where it hinges that has a screw ring on it , have seen corrosion in the plug terminals cause the same problem you are having with the hydraulic pressure sensor shut down ------- I'd also bet you may be fighting more than one problem at the same time ---- good luck ---- fishfiles