overheating

my 1991 caprice 5.0 engine keeps going hot after i have replaced radiator,radiator cap,water pump,timing chain,fan clutch,thermostat,coolant sensor,temperature sensor,timing was checked,no coolant traces in oil,car runs good and mechanic says compression is good,please anyone help me thanks Rafy.

Over heats at idle or while moving??

If it's fine at idle or slow speed, but over heats at highway speed, your lower radiator hose is collapsing and restricting coolant flow.

I agree, that makes a lot of sense. The lower radiator hose is the hose that gets the "sucking" pressure, ad when it ages, it becomes weaker, and often times can collapse, causing a lack of coolant flow, thus overheating.

Nyet. It could happen, but I am giving my vote to a plugged catalytic converter.

Another symptom of this is the car losing some power at higher speeds (freeway etc).

my 1991 caprice 5.0 engine keeps going hot after i have replaced radiator,radiator cap,water pump,timing chain,fan clutch,thermostat,coolant sensor,temperature sensor,timing was checked,no coolant traces in oil,car runs good and mechanic says compression is good,please anyone help me thanks Rafy.
It is while running the car that temp goes hot,at idle it keeps temp at half point.Rafy

In the old days they installed springs in the bottom hoses just for that reason,Good luck
Also if this car has air conditioning check the condensor core for air flow make sure its not bent or dirty.