I recently sold our '99 S10. It did a good job of
pulling the TM. In fact, the power to weight ratio is better than it is on our current full size p/up with a V8.
Without a WDH, it was a little scary when it came to hard stopping. With the WDH, it was tolerable.
The problem is, the TM is heavier than the S10. The ~500# tongue weight takes a lot of weight off of the front wheels of the TV......
Look under the truck and count the # of u/joints on the drive-shaft. If it's a 5-joint d/shaft, it may not last long towing. I replaced mine with a 3-joint d/shaft and it was a great improvement.
I also suggest switching to synthetic oil in the transmission. If you're interested, I can walk you through the changeover. It isn't hard.
I have to think that your 6" sag may be a guestamate..........I don't think that truck has 6" travel. Mine sagged about 1.5" the WDH took care of that.