Car hesitate in any gear when warms up

I have replace the fuel pump, fuel injectors, fuel filter, fuel regulator, TPS, idle control valve, MAP sensor, ignition coil and cables, etc. That car has no catalytic converter and no engine codes. One thing I have notice is that when is cold runs better than when it warms up when cold I can the rpm's up to 3,500 as when warm will only go as high as 2,500 rpm's, and when cold will run up to sixty to seventy minutes as when warm will only go up to 55-60 mph. Another thing I have noticed is than when I clean the throttle area and intake manifold the problem seem to get better. I have check for vacuum leaks and nothing. I am guessing either a gasket is bad when it warms up or I have a leak somewhere that I cannot find. Any ideas will be greatly appreciated?