Can anyone tell me the difference between these engines?
My son has a 2004 Grand Prix GT with a 3800 Series 111 motor in it & My 05 Bonneville is only a Series 11. I would think they upgrade the motors at the same time. Or is it because the Bonneville was being faded out?

Basically, the lower halves of the engines are the same. The upper intake manifold on the Series III is aluminium as opposed to composite plastic on the Series II. Adittionally, the Series III is drive by wire, in other words there is no accellerator cable, it is an electronic/electrical link between the gas pedal & throttle positioner. There may be other differences, I've pointed out the major ones. BTW, Welcome to the Club.

Only the Grand Prix got the Series III motor.

Thanks for the reply. I like paying attention to the different features on some cars and comparing them. I'm not real mechanical savy about cars. I also own a 2000 Impala LS with the 3800 series 11 engine. So far i've noticed that my Bonnie doesn't feel like it has the same power as The Impala or my son'* Grand Prix. I don't know if it'* because of the gear ratio or what. From the comparisons i have made the Impala and Grand Prix The Final Drive Axle Ratio (:1) was 3.05 supposedly 2.86 for the Bonneville. But i also read that with the Leather Seat package the ratio would be upgraded as well.

There are like you mention other factors like gearing and weight that would change the feel of power.