What's wrong with my Ford Ranger?

1990 Ford Ranger 2.9L V6 4x4 Automatic. Happened overnight. One day it was running amazing, the next not so much. Symptoms:
* Won't go past 55 mph
* Delayed shifting
* Loud sound as if air is escaping while accelerating
Beyond that the truck still drives great. No smoking, overheating, nothing else at all.

Check for vacuum leaks. Also, what is the cel saying?