74 Duster - I want new gears! 3.91

Looks like I have a ford 9 bolt rear end.
However my gears seem bad!
Turned tire once and the drive shaft didn't even rotate 2 full turns! Took turning tire about 1 and 1/4 times for the drive shaft to turn twice.

Take a picture and post it. You probably have a 8 3/4 diff.