Yes it sounds to be in limp mode. They use an electronic gov and we did have some problems with the gov solenoid and pressure sensors as I have replaced my fair share. They also use an output shaft speed sensor so the PCM knows the driveshaft speed. But it could also be something else. A good shop can check it with a scanner and the normal trans testing. Its still a hydraulic auto but has the electronic gov that has the PCM (computer) control gov pressure and the trans shifting. It also still uses a cable opperated throttle pressure. And as was said it may have set a code but they dont always set a code. You can read the gov pressure on a scanner and compare it to a mechanical gauge if you have one and hook it up. Any good trans shop should be able to diagnose it for you and tell you what it needs. Ron