MHA is the code for a 3.73 gear. Usually, a Posi differential will have a tag on one of the cover bolts stating to "sue limited slip fluid only", but it's not unusual for those to be missing. To check without taking the cover off, jack the truck up and support on stands, put the trans in gear (any gear will do), then turn one of the wheels (doesn't matter which one). If the other wheel turns the oopsite direction, it's an open diff, if you can't trun either wheel, it's a Posi. Most likely, thouhg, you have the open differential, which as far more common.
