97 Bravada - 90k -tranny - Hard Shift Into 2nd

1) Check tranny fluid level, but be sure to check it correctly. Take it for a short drive and then place it in park and check it with the car running. Make sure you are on a level surface when you check the fluid level. The correct fluid level is a big deal when it comes to the proper operation of the tranny.

2) Check the condition of the fluid. Is it red and clean or brown and dirty? If it isn't red, do a fluid and filter change. That can make all the difference in the world if you have a minor tranny problem. Transmissions run on hydraulic pressure, so the fluid condition is very important.

3) Check for vacuum leaks. Not sure if your tranny uses vacuum to shift from first to second, but check any vacuum hoses leading to the tranny.

4) If the first three things are okay, you will have to replace something. This is a guess, but I would replace the TPS (throttle position sensor) first.  It's on the throttle body and not hard to replace.

5) Your guess of a bad speed sensor is a good one as well. But check your cruise control first. If your cruise control is operational, then it probably isn't a speed sensor. I think all cruise controls operate off of the speed sensor(s).

6) Replacing the valve body would be better than dropping in a rebuilt tranny, but I'm not sure if that would help. You could remove the valve body and clean it up. If it's full of metal chips or other debris, that might be the problem.

7) You can always take it to a transmission repair shop and let them tell you what's wrong and then fix it yourself. They'll most likely tell you that your tranny is shot and you need another one, since that's how they make their money! But you may find an honest person who will tell you what's actually wrong with it.