That somewhat surprises me you broke the sprag, even after it was rebuilt. Mine was rebuilt only replacing soft parts with better steels/clutches, mine already had 34 element sprag (instead of the typical roller clutch), and of course a HD2 Trans-Go kit. I have a billet 9.5" converter, 3600 stall.
My Blazer weighs about double what a S30 does too. My new setup will be pushing around 700 to the wheels (Turbo 6.0) and I even warned the trans builder, but he said its good to 1,000. I guess I will find out after I get it dyno tuned this week.