Why does my acceleration lags gradually gains speed and transmission

i have a 2003 3,8 v6 ford mustang thus far ive replaced the e.g.r valve thermostat upper radiator hose, new plug, new wires, ignition coi,l m.a.f sensor, throttle body sensor, fuel filter, manifold head gaskets, havent checked the cats yet. i read up on it is it possible it could be the toque converter clutch solenoid? its almost over whelming in relation to all the sensors that could be the possible culprit. need help please also when starting in 1st its an automatic transmissions sluggish with the acceleration and i m having to release pressure on the pedal before the transmission kicks down?