Hello everybody. I've been having a problem where my truck (2000 5.4L) feels as if it did not wan't to shift out of first, and into second. It will keep revving up, no matter how hard or soft I press on the pedal. I have to basically trick it into shifting by getting it up to around 2500 rpms and let off the gas. I checked the fluid, it's a good color and filled to where it needs to be. If this has happened to anyone else, or if anybody could help me out, it would be much appreciated! Thanks!!

--EDIT-- forgot to mention, currently has 136k miles. bought it at 125k-ish unsure if previous owner has done a fluid change.