Will it cause any damage to the trans to shift between drive and I (not even sure what I stands for..)

There are two huge hills to drive down in my town. Rather than ride my brakes the whole time i usually shift to I and let the engine take care of slowing me down. But is it hard on the trans at all to do this without stopping first to shift? usually i am shifting at around 35 mph or so.

 

It's acutally better to do that than ride your brakes down a hill. It won't hurt your tranny - if you're in danger of over-revving, then computer won't downshift even if you want it to.

 

Drive = Drive.
I = Intense (Higher RPMS, Harder Shifting)
L = Low (Lower Gear Ratios, Max RPMS, Hardest Shifting, No TC)

 

I=intermediate. it basically eliminates overdrive.

drive is for normal, obviously. you'd used the "i" setting for hilly areas or if for some reason you didn't want overdrive (i used to do this in the snow so that the car wouldn't kick into OD and lose power that it needed to dig through small piles of slush) and L you'd use for very low traction areas. like if you were in sand or snow and needed to dig out and didn't want traction control or the tranny to shift and lose momentum.

an auto matic shifter works like this.

L will allow first gear, that's it
I will allow it to shift from first to second to third
D will allow it to use them all.

AFAIK, the computer will allow more RPM in L or I than it would normally, that is to say, it will wait longer before shifting normally.

 

Nice to see that you haven't driven an automatic Cobalt.

L Handles 1st and 2nd. Cuts fuel at the end of 2nd.

There's a whole thread on this.

Downshifting into I won't hurt the tranny... as far as you don't over-rev it by shifting at too high a speed.

I usually do it at about 40-50 MPH... use it for passing and slowing down... makes my exhaust gargle nicely on the decel too.