1999 Chevrolet Blazer

Transmission problem
1999 Chevy Blazer 6 cyl Four Wheel Drive Automatic 130000 miles

I recently lost the ability to shift into drive and overdrive. The transmission works fine from a stopped position, until it goes to shift into drive. It acts as though that gear doesn't exist. I had to drive it about 15 miles back home in 3rd, and upon returning home the fluid smelled very hot. Am I going to need a new transmission? Thank for the time. I have only put about 30k miles on this vehicle. The engine was replaced when I purchased it with a new crate motor. I have not changed the transmission filter since I have owned it. This problem also seemed to start at the same time as I had to replace the Throttle Position Sensor due to a engine code.
May 11, 2009.

You should be getting a check engine light on
and if so have to have it scanned for codes
let me know what you have for codes
also if to be using a scanner check for tranny codes
and OBDII codes will be ok too
let me know

need manual CHECK IT @

May 11, 2009.
When I replace the throttle position sensor, the people at the autoparts store told me that the code had to reset itself. Is this correct? Or will I have new codes now?

May 12, 2009.
You should have a new codes know
plus you should’ve reset the codes after the repair was done
check for codes 1st let me know what you have

May 12, 2009.
The new code I received was P1870. It was in twice.

Jun 13, 2009.

Circuit Description
PCM monitors difference between engine speed and transmission output speed. In D3 with TCC engaged, engine speed should closely match transmission output speed. In D4 with TCC engaged, TCC slip speed should be -20 to 50 RPM (all models except Corvette) or -20 to 40 RPM (Corvette). DTC P1870 is set if PCM detects excessive TCC slip when TCC should be engaged.

Action Taken By PCM
PCM performs the following if DTC is set: Will illuminate MIL at second consecutive failure signal.
Inhibits TCC engagement.
Inhibits 4th gear if in hot mode.
Freezes shift adapts from being updated.
Commands maximum line pressure.
DTC P1870 will be stored in PCM history.

Jun 15, 2009.