TD5 engine starts and sounds good but no power

Because I decided at nearly 70 to hang up my spanners I have had the head gasket done by a friend. Now my td5 will start immediately and sounds good but has no power. I have got my spanners out and tried to help Checked and double checked the timing. Had the injectors checked on a machine to make sure they were matched to the ecu. New fuel pump and filter already fitted.Removed wiring harness back to ecu. cleaned and checked all the wires for continuity as well as injector harness. Checked fuel flow and pressure. Had it checked by another 2 computers. Turbo works perfect except the waste gate does no open. Now at a complete loss what to do next. Can any one please help.
Bob

Hello and welcome!

Disconnect the MAF and see how you go...

ALso, what vehicle? D2 or Defender? And what year is it? If it's a 15P D2 it might have a CAT in the downpipe, these can block up and cause it to have no power at all...