Hello anyone, in need of a little assistance. I have an 04 Grand Prix GT 3.8L ,regular not supercharged, and had a 06 motor installed with the same transmission. The motor had originally 75,000 mls on it they say. But the transmission is shifting out slow as if its straining the motor to shift out. This didnt start happening til after they installed the 06 motor. What could be the problem? Could had the mechanics did not sink the motor with the transmission? Or I just need to change my filter b/c I havent done that yet but I will do that this weekend.

 

The first thing i would check is the transmission fluid level. It's possible the mechanic didn't fill it up all the way. Try adding some fluid to see if it gets better. If you change the filter, you might as well just change the fluid while you're at it. Are there any codes stored, or a check engine light on?