My SE-R hates to go into DFCO. It has to be in closed loop, engine warmed up, over 2500 rpm, and in gear. If that gear is top gear, that means I have to be rolling over 65 mph, with no FASing within the past 4 minutes, severely limiting its likelihood of entering DFCO. It also hates to stay in closed loop. If I FAS, it goes into open loop, and takes four minutes of constant running to go back into closed loop.
My xB, by contrast, goes into DFCO easily. It has a 1500 rpm DFCO bottom limit, which translates to 35 mph in top gear.
That said, I rarely use the transmission to decelerate. I almost always want to maximize coasting distance, rather than limit it. The .11 to 22 gph hit I take for less than a minute a day by not DFCOing doesn't add up to anything.
My truck goes into DFCO rather easily, and I used to downshift 1 gear when approaching red lights to keep DFCO active longer, but I stopped most of that after I had to pay for some transmission repairs. I was unsure if my transmission problems were related to me downshifting to maintain DFCO.
Actually when aproaching a red light try to prolong the DFCO as long as possible since the longer you stay in DFCO the more time your engine is not burning fuel as you wait for the light to turn green.
That's perfect if you know you'll be stopping. If you think you can roll through a green light you're better off sacrificing DFCO in favor of whatever braking is necessary to maximize your conserved inertia. It's better to roll through at 15mph than to DFCO, if you have to choose.