Try this scenario: There is a variable control switch in the transmission that tells the tranny-computer loop where the throttle is once the throttle is opened a bit. That switch has the cable from the throttle body actuator arm attached to it. If that cable is out of adjustment or the switch is screwed, the transmission doesn't know whether to scratch its watch or wind its ass, and the computer will limit the engine speed if the input signals are way out of bounds. Eventually the Check Engine light will rear its head.
Go to the throttle arm end of the cable and take a close look. Look for the little metal piece crimped onto the exposed portion of the tranny cable near the throttle actuator arm. The little crimp should just show its outer edge past the end of the cable sheath with the throttle closed, and don't let it worry ya, but that cable should leave some slack in it.
Best case scenario, the cable is disconnected on one end, or the cable is adjusted too loosely. Worst case scenario, the cable wasn't adjusted properly, is too tight, and the switch has been pulled apart inside the tranny. Most likely, that cable or the switch is the problem.
These transmissions will easily go 200K miles with reasonable care and maintenance, and I speak from three experiences on that. If there's a weak point, it's the same as most autos: big tires and high gears building heat and stressing the torque converter and, as Stankoma can testify, breaking flexplates. If you off-road it, keep it cool and just change the flex plate at 100K and save yourself the shoe leather.
