Why wont my truck start without popping the clutch?

might be clutch dragging, when you are trying to start it is trying to turn the diff. by popping the clutch you are separating the engine from the gearbox, then the starter is only turning the engine over. with the clutch in you are getting higher turn over revs and your truck starts. this may have been your original problem 20 months ago, you may have fitted new parts that then hid the real problem until now.