Belt for my IDI

Hey guys my old serpentine belt snapped on my 7.3 IDI 1993, so i bought a very nice belt thinking it was the right one. it was the good year Gator back and it was 113 long. truns out when i put it on the belt was too loose (later found out that belt is for the AMBULANCE package with the leece alternator...which i don't have), so i went to the nearest autozone and bought some cheap belt that was 110 long.the only thing is when i put it on today i drove the truck for about 2 miles and the belt snapped and ripped to shreds.

was the belt too small?
is there a special kind of belt i should buy?

please help....

thank you.