transmission question

Last month i was having trouble with the transmission slipping and not working right i talked to some people and changed the transmission fluid and filter and the problem went away. Im afraid that the problem is starting up again no matter how much i hope it isnt. Does anyone have any ideas as to what the problem might be.

Need more info on when and how the slipping and " not working right" means and when it happens. How about year of truck, you must get used to posting pertinent info for any comprehensive help here

88 4wd by sliping i mean when accelerate it sounded like i was reving my engine but i got no power, by not work engine worked but i went nowere

Does it also slip in reverse?

Does it slip if you manually select 1st or 2nd range?

Do you feel positive engagement when moving between reverse and drive?

Any unusual buzzing, whining, or other sounds? Is the fluid level correct?

yes it slips in reverse, manualy selcting that im not sure about, yes i feel engagment, and yes i made sure the fluid level was correct