Never seen a Class IV hitch for an Astro/Safari. Our towing capacity is only as high as 5,500 lbs.
There are different weight ratings on different Class III hitches, however. Just get the highest-rated Class III.
I took a Class I hitch off my '99 when I got it and put the Class III that was on my '93 when I bought it.
The Draw-Tite Class I I removed:
And the Draw-Tite Class III I installed - but not until after I wire-wheeled, rust converted and painted:
That is the hitch I moved to my '02 and used to tow my Jeep Liberty home on a Uhaul car trailer, which weighed in at 6,250 lbs together.
Beefier construction all the way around, more frame bolts (and longer section) and bumper bolts.
Please note the note on the label -"Do not cut, drill, weld or modify." To get the higher weight rating of the hitch, you must use weight-distributing stuff.
The one that came installed on my '05 is very similar to the Class III above, same weight capacity and same construction.