99 Blazer would have a NP233. Same as a NP231 with the exception the second 3 signifies that it is electronically controlled. Very good t-cases in a light weight rig like ours. This is also a part time chain driven t-case with a 2.72to1 low gear. I dont think there is a lower stock low range, except the new Rubicons which come with a 4to1 low range.

NP208 was in the fullsize rigs before the NP241, and now they use a NP243. 2.62to1 gear ratio.

NP207 was first in the S10, then NP231, and currently NP233. 2.72to1 gear ratio. We have a better low gear then the fullsize rigs.

To figure crawl ration, multiple the tranny low gear ratio (3.06 for the auto), times the t-case low ratio (2.72), times the differential gear ratio (3.42 in my truck)= 28.46to1 for a crawl ratio. If I had 4.10 gears it would be 34.125 crawl ratio. Not bad for a stock rig.


To verify which t-case you have for sure. Crawl under the truck and read the tag on the back side of the t-case. Its round and has the model number stamped into the tag.

Then do a websearch for New Venture or New Process t-cases. They have a break down of what the numbers mean.