slugman,
I upgraded to the rifled storm series this spring, but for years used the smoothbore Model 37.
Some of the things I know...
Ithaca's iron sights are some of the most accurate you'll find on any gun. They are deadly accurate to 75 yards. I sight in at 50 yards, and at 75 yards it drops by ~1 inch.
If you have Remington slugs, you may as well throw them in the garbage [

]. I, and about 6 friends who have Ithacas, have never been able to get a Remington slug to shoot accurately or consistently from the smoothbores. The rifled barrels are another story

.
I found that Federal, Kent and Brenneke slugs performed the best. I always took Federals into the field. I'm also assuming that you have an older M-37, so be sure you only use 2 3/4 rifled slugs, its not chambered for 3's or sabots.
Hope this helps.
S&R