thank you for replay..so, it is a 1990 Jeep Cherokee, 4L engine, 6cyl in line, 220.000 Km on it.
Jim if you refer at air filter, last change was ~15.000 km ago.
The transmission oil level is between add and max, so is ok.
I want to mention that all this hapend after I wash the engine and under the car.
Can be the transmission speed sensor? If so, where is it?
The main sympton is that the first gear changing is to late(~60km/H)

Thx a lot.