Sorry... I guess I wasn't directly answering your question. I know what the 355 chassis vehicles are... I was just speaking in general why they might want to use this instead of the I5 for other models (space contraints).

For the 355s, well, the I5 only makes 220hp and 225tq. That's quite a ways below this new DI/Turbo 4, plus I'd be willing to bet that the DI/turbo 4 gets better gas milage to boot.

The 2.0 in my audi is DI/turbo but only 200hp/207tq. Still, for a car that weighs as much as my A4, I've been getting 28.5-31mpg, 90-95% CITY driving and beating the ever living crap out of it quite often.

I'm impressed!

You say the I5 will be getting a displacement bump... and did the math, but the previous 3.5L doesn't match your math - it comes out about 25 horsepower higher than it really is. So what's going to change that will affect that other than displacement? I double it'll be more than 260/260 and even if it were, what's happened to gas milage in the process? The I5 is already not very competetive in the realm of gas milage compared to other similar sized trucks. It doesn't need to get worse while the other trucks are getting better.

 

The original Atlas inline 6 produced 275 horses - and was bumped for the '06 model year to 291 horses (via higher compression and improved airflow).
If you do the math, the 5cyl 3.5l, based off the original 275hp would be 229hp -- pretty close to the 220hp it's rated at now. The 3.5l in the Colorado has the same compression as the original 275hp 4.2l I6. If the 3.5l was given the corresponding improvements, the 3.5l would push 242hp -- bumping the displacement by 0.2, all things being equal, would move it towards 256hp. Not at all bad for a 5cyl.