hi I got 97 4x4 blazer, At first I got Service Engine light, Checked code it was transmission slip code, I replace tram fluid, reset code and it stay off for a while, than it came back, after several days came off. Next problem with my 4x4. When I switch to 4 hi it feels like it stays in 2nd gear , when I try to go back to 2 whd nothing changes the truck stays in 4 whd. I accelerated to about 50 mph and I felt a switch to 2 whd and rpm drop.

 

You really should diagnose that transmission code. I assume it was P1870 - Transmission Component Slipping and if that is the case, there are a number of discussions on the forum about that code so a search will also turn up more information for you.

As far as your 4wd, please be more specific with your explanation of what is happening.

It stays in 2nd gear..? Like the transmission stays in 2nd, not shifting into 3rd? Nothing in the 4wd system should cause the transmission to freak out.
Does the 4wd engage?
Do the lights on the dash work?
Do they blink after selecting a new mode and then go steady?
When on a low traction surface (gravel, snow, sand, etc) does the front axle pull?

For more information on the NV233 transfer case, check out the Tech Article (DIY) section as well as run a search for "NV233".