Well it has no real fueling control with no front o2 sensor, just a basic open loop limp type mode for fueling if you had to drive it. That's why just a quick drive up the street and back to see if you could power over 3,500 as a test and come back.
Not sure what to tell you now if it runs okay but can't make it over that rpm. The transmission is the next thing to look at. Make sure it's got proper fluid level, past that it could be an internal problem with it.
Without it in front of my with a scan tool I can't diag this stuff from a keyboard.
