I just hit 100,000 miles and when I go to accelerate.......as soon as it hits 35-40mph it hits the rev limiter and the tach won't go over 4Krpms. If I let off it runs fine and gradually gets to speed. I stopped vehicle, shut off and restarted and it didn't seem to come back. I'm thinking something in the transmission in 1st gear is going out. Any ideas??

 

from what ive read, not personal experience. its the sensor for park/neutral. in park or neatral these 3rd gens rev limit at 4k. thats my best guess.
cheap electronics and sensors on these trucks aka unreliable