wont rev up

hi guys ime new to the site and was wondering if anyone could help me,ive got a 95 disco tdi,and it wont rev passed 2000,it all started when i took it to a garage to have the boot floor welded up,when i drove home doing 30 limit it was fine,but the next day when the misses had to hit the maximum speed limit on the way to work,you cant get it passed 35-40 mph,it starts to splutter and the revs drop,so i took it back and they said with having to drop the tank they might off disturbed the **** at the bottom up into the fuel system,so they took the tank off cleaned it out,cleaned the water trap out and changed the fuel filter.but not its just the same,it wont drive over 30 mph and when i ring the garage they tell me they dont know what to do next.please help

I had similar issues, ended up running a hose direct from the tank to the lift pump, bypassing the sedimenter, which has made it run like new

Must have been a blockage in the pipe or the sedimenter!

could be they damaged the fuel line where it enters the tank. The fittings can become fragile and the metal bends going into the tank rust a lot over the years and you may be drawing air into the fuel line causing poor running.

Lift the boot floor carpet and remove the inspection plate above the fuel tank and have a look at the pipes. Could also be the sedimenter problem as per previous reply.