In the first two seasons, Lamont was past the point of being rude to Donna, but by the end of the series they seem to have reconciled their differences. I know the reason for this was because of the many script writers over the years, but what was the storyline explanation (if any) and in what episode?

There wasnt any explanation, it just happened for no reason.

Fred was really sweet to Donna in the later epsiodes. Fred was the one who treated her like crap. Fred got his though when he became attracted to a woman who was actually a man.