1998 Other Rover Models My truck does not pick up speed fast

I took it to the shop 4 times for my truck not shifiting gears fast enough. I have a used newer transmission,valves,tune-up, and new gaskets for my bad oil leakage. The porblem still has not been fixed. Another Land Rover owner suggested I might need a fuel filter. But will this help my car to move faster without me pressing the gas pedal all the way down? And for my RPM gage to stop moving by itself when I am driving?What could help my car to move at a better quality performance ,instead of stalling like it dont want to move? I told the shops many times that my RPM gage does not start from "0" like I know it should. I revs up to high when pressing the pedel because again it takes along time to go to the higher gear. I have an automatic not manual so I really dont know what else it could be besides the major work I alreadt did. I belive it is a smaller problem that can be fixed without hopefully without going back to the dealer or another foriegn shop. Please HELP!!!!