sounds like boost control solenoid problem
around the town you wont be holding boost pressure for long enough to get engine management worried ,
on a fast road getting up to speed and cruising anywhere over 3000 rpm the turbos pressure will climb and trigger the manifold absolute pressure sensor because the boost solenoid problem wont be opening the wastegate to stop overboost,
the vauxhall will go into limp mode with a few dash lights coming on and not letting engine rev above 3000rpm, until you reset the fault by turning off engine and starting again.
check boost control solenoid / hosing and wastegate diaphragm or siezed linkage on top of the turbo.
this could be the reason your last engine blew by running high boost pressure / lean running
also when you changed the engine did you get all the hoses correct?
robbie-mechanic
September 2010