2005 MAZDA MX-5 MIATA Engine And Engine Coolingengine Problems

I PURCHASED A USED 2005 MAZDA MIATA 5-SPEED IN APRIL 2006 WITH 7860 MILES ON THE ODOMETER FROM THE LOCAL CHRYSLER DEALER. I HAD NOT DRIVEN THE VEHICLE OUT OF TOWN UNTIL OCTOBER 2006. ON THE INTERSTATE HIGHWAY I NOTICED THE VEHICLE HAD INADEQUATE POWER TO SAFELY DRIVE AT THE SPEED LIMIT (80 MPH). TOP SPEED IS ONLY 82 MPH @ 4200 RPM IN FIFTH GEAR (SHOULD BE 120 MPH PLUS) AND ACCELERATION UP A HILL IS BAD. I MUST DOWNSHIFT AND FLOOR THE ACCELERATOR TO MAINTAIN SPEED UP HILL AND THE CRUISE CONTROL WILL NOT HOLD THE SPEED. TRYING TO PASS A SLOW VEHICLE UPHILL IS ALMOST IMPOSSIBLE. THE VEHICLE IS IN THE LOCAL MAZDA DEALER'S SERVICE DEPARTMENT WHERE THEY HAVE NOT FOUND THE CAUSE OF THE PROBLEM. I HAVE HAD THE VEHICLE SERVICED AS REQUIRED AT THE MAZDA DEALER AND HAVE EVEN REPLACED THE AIR FILTER WHEN NOT...