Have had this problem for awhile and would really like to get it fixed. Took it to the garage and they said that the tranny was goin bad. Go figure. But the fluid is still red. It runs fine from a cold start, and then seems to happen after it get warmed up. Usually while driving seems to get stuck in gear, it just revs high then spedometer drops out and have to shift to manual 2nd and drive it that way. Then once i get goin the spedometer goes up and sometimes it will work if i shift back into drive, but only till i slow down the acts up again. Havent scanned for codes or anything. Tried cleaning the vss. Just seems like somthing that doesnt require a rebuild or new tranny. Maybe thats just wishful thinking. Any suggestions would be greatly appriciated. Also might be related is it did use slip shifting from first to 2nd, but as strange as it sounds that went away after i got a underbody wash a few weeks ago. By the way its a 97 blazer 4x4 automatic.

 

I had this very same problem with mine and I to tried cleaning the vehicle speed sencor and it still didn't work so I bought a new one and she came back to life just like new . Mine is a 94 so I think there a little different , your bolts on and mine screws in , I think . But if yours does screw in pm me and I'll send you my spare one its brand new . I thought mine went bad again but it was just a loose wire but I traded in my old one to advance for a core so now I have a extra that I don't need because it's warrantied .. Or you may just have a loose or dirty wire down there like I did .

 

Without a good VSS (vehicle speed sensor) signal, the transmission will not be able to shift properly. The fact that the speedometer is dropping out points to a failure of the VSS and/or it's wiring. The sensor can be removed and cleaned as suggested above and that is relatively easy to accomplish.

If that doesn't work, then you have two choices. 1) test the wiring to/from the VSS or 2) replace the VSS and hope that was the problem.

 

Check your +12v connections (battery and alternator) to make sure you have good power to the system as well.

 

Thanks guys let hope thats what it is. Then some new tires and some body work and ill be good to go.

 

found one so dirt cheap on carpartswholesale.com....anyone think that would even be worth trying? Also any advice on the best way to check the wiring...step by step if possible, as im not an electrical whiz.