lugging problem

Got a 95 Contour SE 2.5L 5 spd manual, with 154,000 miles. The clutch was replaced at about 145,000 miles. Most of the miles are highway, and in the past few months it's only been driven a few hundred miles.

Recently when I've driven it the engine has been lugging in 2nd and sometimes 3rd. I'm doing anything different in my driving, so I have no idea why this is happening.

Anybody got any suggestions on why the car would lug besides driver error? It is running fine in 1st, 4th and 5th. Also, I took it up to about 40-45mph in 2nd gear (5500-6000RPM) and it did this like it always had, smoothly (for those of you without the V6, the peak torque at 4250RPM sends the car flying, and even this is smooth).

Thought I'd mention this also, though I have no idea why this would cause a sudden problem like I have. I noticed the serpentine belt is cracking, where the "teeth" on the belt are, its starting to crack. The flat side is fine, though.

Belts would cause slow problems, though, and this literally happened overnight. It wasn't lugging on Friday afternoon, and was lugging real bad on Monday morning. By the next Friday, it was still lugging, but not as badly.

I've probably put about 5 miles on it since it started lugging, though.

The only thing that was different than usual on that weekend it started lugging is that the car was left outside during a heavy rainstorm. The passenger side floormat got wet, obviously there's some leak I can't find.