I have the same question as you ^^
Coming from the Jeep world, I'm very familiar with gear ratios vs. tire size for the dana 44's and the weak 3.8L v6 with 5 speed tanny.
Just picked up my '14 CC w/8 spd & 3.21s about a month & a half ago, and the 5.7L & 8 spd is a whole different world. I went from 275/60r20 (33") stockers to 295/60r20s (34.45") and now the truck is sluggish, along with losing about 2 mpg. I was thinking about a programmer to correct for tire size which should correct speed and mpg reading. But, it doesn't solve the sluggishness of the truck.
Looking for any experience with gear swaps from 3.21s to 3.55s or 3.92s. I'm just looking to get back to stock performance, so thinking the 3.55s could work. With the 3.21s & 33" stock tires, it was plenty peppy. I had to actually feather the throttle because I would routinely chirp the tires from a dead stop. I know it should run close to $1800, but I can't find front 3.92s or 3.55s. Only for the rear. I looked at MOE's but I must have missed them. I've seen some '13 front & rear axles for sale with 3.55s. Wondering if I should just swap them in?