I made a habit of turning O/D off whenever I turn the truck on (towing or not) , due to my 3.55's and the fact that the O/D unit sucks to begin with, let alone turning the big meaty tires. My Q is, will I finally be able to use O/D when I'm not towing when I get the 4.88's in?

 

yes.

assuming you have a 1500 that came with factory tires 225-75-16, the tire size calculator says they are 29.3 inches in diameter.

38 / 29.3 = 1.30 tire change from stock (30% increase in tire size)

4.56 / 3.55 = 1.28 almost but not quite a return to stock.
4.88 / 3.55 = 1.37 7% gear reduction from stock. a good choice !!


for those of you with 285/75-16
32.8 / 29.3 = 1.12 12% increase in tire size.
3.92 / 3.55 = 1.10 almost but not quite back to stock.
4.10 / 3.55 = 1.15 -3% gear reduction from stock.
4.56 / 3.55 = 1.28 -18% from stock
4.88 / 3.55 = 1.37 -27% from stock