Transmission rough shifting

i have a 1993 3/4 ton pickup 5.7 and it just started to shift rough it has to get up to 4000 rpm to shift from 1-2 and 2-3 someone told me to change the filter another person told me to check the vacume line i went under truck and found a vent tube out the side not sure what to do

You want to look on the transmission and find a vacuum hose plugged into the side of the transmission. This hose is connected to the transmission vacuum modulator. Remove the vacuum hose from the modulator, and if transmission fluid leaks out of this connection replace the vacuum modulator on the transmission.