S-10 transmission slip

98 Chevy s-10, 175k miles, 4cyl 2200, automatic; trans started slipping one evening, would barely pull when gas pedal was pressed all the way to floor, but dropping it down in 1st and shift up into drive after gaining some speed, truck would go with no problems. Parked it overnight to take in for diagnosis, the next day it was not doing the same thing. Truck seemed to be fine. Diagnosis showed: map (mapping?) Sensor bad, fluid level high, transmission slipping. Is trans going bad or could the sensor going out be the whole problem? I don't want to spend unnecessary money on new transmission. Help!