93 2.5 liter grinding third gear

i have a 1993 five speed s10 with a 2.5 in it and almost everytime i shift to third it grinds and doesnt want to go in i have to cram it in but sometimes it goes in perfect and when i down shift i gotta wait for the rpms to go way down before it will go in and by that time i need to be in a lower gear please let me know what it could be. thanks