Lack of power ,no O/D ligth

[extex]

I have a 1993 land crusher,and it has no power when I press the gas to the floor but only beetwen 20 and 30 miles ,after that and before that it does ok. I was trying to get the codes from the computer but my O/D ligth is out ( but i know that the ligth is good cause I already checked it and I checked the O/D switch as well) so I don't know what to look for ,I have replaced the transmission fluid/filter ,spark pluhs ,wires ,rotor and also a small crack in the air intake. so what's next? any body has had the same problem?.