when i tried to go up hill the speed will go down to 10m/h ,and sometime while on flat land the truck cant pass 30m/h.
Have the fuel pump pressure tested to determine if it’s within specs.
Tester
Of course, change the fuel filter, first. A dirty fuel filter can reduce fuel flow.
You can also get the computer codes read and maybe there will be some kind of hint coming out. There are many things that will cause low power.