lopezSR5

i have no idea what to do, my transmisson is going crazy i will put it into drive and press the gas to go but its like its bogging down. almost like first gear is slipping but it will still move then when the tach. hits the top of fist gear it will shift and drive normal but it wont go over 2000 rpms im going to change the transmission fluid out tonight and clean the "speed sensor" if thats the correct name for it but im going to give that a shot and if not im out of ideas.

but if anybody know what else it could be im open for suggestions. but i drive a 99 SR5 2wd with 224,576 miles on it thank you lol. if anybody else has had that problem what did you do to fix it without going for a new transmission