Cat D5N 2004 serial number AKD00796 when you first crank it up the RPM will slowly increase to the 2000's then when you mash the decellorator and release it it will slowly increase to around 1300 I have replaced both fuel filters and the fuel lines coming from the tank to filter , ckecked return line orfice , checked fuel flow out the tank through return line , and hand pumped the fuel through it out of the open fitting where the return line check valve goes with a good flow of fuel what should i check next Thanks
Throttle linkages free and lubed,return springs working not stretched or broken.