1.9l the beetle will not go more then 55mph
55mph on 2000 Volkswagen Beetle TDI
Your car is going into limp mode? Do you have a CEL? It could be a number of things causing this...Clogged fuel filter, clogged intake manifold, vacuum leak, turbo, etc. I would have your car hooked up to VAGCOM and check for fault codes.
my car done the same thing. It was due to carbon build up in the head. Take it and get the head decarboned.