I have this same problem with my 04' CrossFire!!!

It is always stuck in limp mode. Before it would slug into each gear...then only 1st and 2nd gears work, now ONLY 1st gear..cant drive it faster then 45ish mph.

I replaced the Transmission Speed Sensor, from the dealer it was $340. and the electrical plug I replaced while at it.

BUT it never did anything different for me, replacing the Transmission Speed Sensor didnt change anything. It is a black plastic plate that attaches to the valve body inside the Transmission...What do I do now?!?!

Sad to say, with other vehicles to drive (I have babies, an SUV is a must) This car has been sitting out-of-site, out-of-mind since July of 09'!!! Its time to get this thing back on the road!!!

Thank You all in advance for your insight!!!