2001 Tacoma transmission problem?

Hi. I have 2001 Toyota Tacoma 4x2 standard bed pick-up truck. For about a year, I've been having this problem with my gear. From stop, when I put it on first gear and let go of the gear handle, gear pops out automatically into neutral. So to remedy this problem, I have to hold the gear in place. I have no problem with 2nd , 3rd, 4th, and 5th. Just 1st gear. Also, from stop, I have hard time putting it into first gear. Again, I have no problem with 2nd, 3rd, 4th, and 5th gear. Anybody have suggestions? Thanks alot.