I have a model 37 Ithaca rifled slug barrel with a three inch chamber..Would 3 inch sabots generally be more accurate than 2 3/4 sabots
No.
You will need to try various slugs to find those which your gun prefers. I have not found 3" shells to shoot any better than 2 3/4" but part of that is the way I experiment finding a load-start with the least expensive load I can readily find and work up. When I find something that keeps 5 rounds in a palm sized group I stop. The price generally precludes 3" shells but I don't miss the added recoil.
The closest I can suggest for a "one stop sabot" is the Remington Accu-tip. It seems to group at least adequately in most slug guns. It is my first choice when I don't have time to experiment with slugs. At $3+ per round it is not my first choice.
My model 87 with 20 inch rifled barrel shoots LiteField slugs pretty well. I do notice when i remove the barrel it needs to be sited in again.
In theory the 3" shell will provide a better gas seal in a 3" chamber, but that is splitting hairs. Slug guns are getting more and more and more accurate, but they are still not sniper rifles.
Years ago I was told that stuff about 3" shells in 3"chambers for the fully rifled 12 ga. 870 I use in shotgun zones. Found out by experience that it wasn't true; at least not in my gun. I run 2 & 3/4" Sabots because my barrel is more accurate with them. Not only that but I also discovered that deer can't tell the difference which slug I hit them with. So I just go with accuracy.