my truck was working fine yesterday(1995 ford Ranger 4.0l automatic i did an engine oil change with royal purple and K&n filter and after i got done i backed it out of the garage fine and then i put it into drive and it wouldnt move. after a while i tried to push it then it kicked into gear and now I have to do that every time I want to go forward. please help

Check transmission fluid level.

its full and all my fluids are new and good

Check the transmission control solinold.

You may have disturbed or damaged something with the vacuum system check all hoses. I accidentally broke one of those shitless tiny hoses when I put my cold air intake on. Took a while to find. Try spraying water or carb cleaner in the area. If there's a leak you'll hear a difference in idle.