Seem to be having some dead pedal issues when in lock up everyone and then. Also seems very sluggish in gears 1-3. Truck has 260k miles. Hard for me to think its the injection pump since the previous owner put an aftermarket BD pump in. Can anyone shed some light on this issue for me. Thanks

 

Most likely it will be your APPS (Acceleration Pedal Position Sensor), its seems to be common for them to go once you get around your number of miles.

 

pull codes from it first to help diagnose the problem...