No power and engine pinging at acceleration

I have a 1995 Mercury Mystique GS, 2.0l engine I got the car with a blown head gasket after replacing the head because it was damaged and the gasket, the car starts and idles good, as soon as you put it into gear it runs rough, when pressing the accelerator it has no power, and the engine pings, the car acts like it is starving for fuel, and drives like you are starting off in 5th gear. once the car gets moving down a hill it shifts through its gears and reaches adequate speed, as soon as you reach an incline it looses all power and pings as it climbs the hill at 10 to 30 mph depending on the incline. I have replaced or tested the following parts.
Torque converter replaced, cat convertor not clogged, ignition coil replaced, plugs replaced, map sensor replaced, fuel pressure tested and stays at 37psi to 40 psi, fuel filter replaced, ECU replaced, MAF sensor cleaned, EGR valve seems to open and close. I am at a loss and can not figure out why it is acting like this and am tired of guessing, oh and I have redone the timing more then once and also replaced the injector wiring harness due to wires cracked from previous owner over heating it so bad, compression tested good in all 4 cylinders does not smoke, does not loose water or oil, plugs look good after running the car, the car still over heats or the temp sensor is bad, have not checked the water temp but it shows on the gage that is is right at the red. any suggestions would be great Thanks