I have a 1994 Nissan Pickup XE King Cab. It loses power. It loses power when going uphill and when I try to pull off . While drving I can only get up to about 40 mph sometimes 45 unless i am going down hill. Also the heat does not work. I've had the thermostat changed and the radiator flused but it always read at the cold lever on the dash even after I have driven for miles. What can I do to solve these problems.