Don't quote me on this, but it sounds like something either got into your valve body or syncros (if autos have syncros, i dont know much about transmissions) Have you recently had it flushed? or have you made sure the transmission fluid level is correct? (second may sound like a dumb question but i've met some people who have no clue.) btw, if you ask here
you might get some more help.
Redfire '04 V6 - K&N CAI, Divorced duals, Bama Tune, EGR Delete, Gauge cluster LED overhaul.