Transmission trouble

[BDever]

My 94 XLT wouldn't shift in to drive today. I'd been driving on the freeway for about 2 hrs. Made a short pit stop, put it in reverse, no problem. Shifted in to drive... nothing. Gave it a little rev, nothing. It wouldn't engage. Put it in park, shifted in to drive and away it went. Drove another 3 or so hours on the freeway, got home, turned it off and unloaded my bags. Started it up again, shift and nothing. Reverse is ok. Tried to put it in 4x4, nothing. So it's parked for now.
Any suggestions on where to start?

 

[Vacdaddyt]

Check fluid level first?

 

[arco777]

Verify the shift linkage is working properly. With the parking brake on and engine off, have someone shift through the gears while you check the linkage underneath for proper movement.