I own a 2000 old bravada when driving wont go into 3rd gear and speedomoter quit
 

I wasndriving on the highway and al of a sudden my rpmsnl shot high amd.it wasnt like i was driving and also at that point my speedometer wuit workinh
.i pulled over parked then tried again as i got to where it would shift into 3rd gear then nothing. So i pulled over again and put the shifter in 1st then shiftednto 2nd smf tried to go int9 third and nothing so it seems that there isnt 3rd gear anymore. Bownindonneedna new exhaust but chose to have the mechanic patch it. I d9nt eant t0 put a ton of money when yhisbisnmy back up car which im driv8ng now until late fall when my.new auto i ordered arrives i
arrives at the end of october. Any ideas. I hate going in to get fixed without someones opinion. 1at i know a dealerahip is gonna charge alot and guarantee they would try and pull.bad tranny bs need new one because im female abd 2nd reason is thats hoenthey make money. I worked for s dealership for almost 25 years ao any ideas that would help me have a rough idea prior to taking it would be gratly appreciated.

I'm new to the Blazer myself but it is possible that a faulty speed sensor is causing your problems. Someone more knowledgeable should be along shortly to help you out.

That is is a good call that perhaps a speed sensor is bad since that might affect both the transmission and speedometer.

A not uncommon problem with our transmissions is that you get a burned out 3/4 clutch-pack. The symptoms are the transmission attempts to up-shift into third and then the engine revs high while there is no drive. It feels as if you have shifted into neutral instead of 3rd. What is going on is that the friction plates for 3rd (and 4th) gear are no longer able to stick by friction to each other and just slip; like a worn out clutch on a manual transmission.

I wonder if a bad speed sensor would set an error code?

I'd suggest going to a parts store and have one of the counter people hook up a code reader to see what the error codes are. Note that the check engine light does not turn on for all error codes so it is possible there is information to learn even if the warning light is not on.

Good Luck