Hello and Help

Hi everyone I am new to this, not really done anything like this before, but thought I would ask fellow Discovery lovers for help as i am at my wits end.
If you can help please don`t get to technical I know nothing about engines. I am currently on my 3rd Disco and it is getting on a bit, 2001 manufactured so a decent age. He is a work horse not just used for shopping. We have horses, so he is used for towing and general farm work as well as carrying the dogs and kids.
Problem is :
When I start the engine in the morning all is well, I do about 3 miles on the schoolrun, when the car starts juddering, I can feel it through the gearstick, it`s almost like slight fuel starvation, or misfiring struggling to pull away and Juddering through the gear changes, doesn`t get up to speed and having to change down a lot. I am sorry but i don`t know how else to explain it.
After a couple of miles arrive at school turn engine off, unload the kids, switch engine back on and alls fine, and stays like this for the rest of the day.
Today changed the fuel filter didn`t make any differance
If I take it to a garage I would like to be able to explain what the problem is, can any one help ?
Any one had the same ?
Thanks in anticipation
Janro

is it petrol???
if so do they have coil packs? and if yes maybe thats starting to fail,but i have a td5 so not really sure

do you have a hawkeye? or anyone near you with one,im stafford if thats close?

Fuel pump on its way out or oil in red plug?