One thing that has not been mentioned is the pilot bearing. I had one go out earlier this year. I typically just had difficulty in getting it in first gear when stopped. It was inconsistent and not always a problem. One evening while going home it started trying to take off while stopped with the clutch pedal pushed in and in gear.
When I took the transmission and removed the clutch, little needle bearings started dropping. I found the pilot bearing was destroyed. Apparently some of the needles would get sideways sometimes and bind on the transmission input shaft. I put in a new pilot bearing and it work like new again.
2002 FX4 Bright Red Supercab 4.0 SOHC, manual 5-spd & Tcase, 33" BFG MTs, K&N air filter, Modified air box inlet, Gibson SS cat. back exhaust, Bama flash, Hidden Hitch round receiver, Rear helper air springs, Electric trailer brake controller, Line-X bed liner, WAAG bar with KC lights and Wildernest shell.