'97 Tahoe speedometer wigs out/transmission won't shift

[Lil Al]

so i'm about half-way home from Lansing (100miles away)
cruise kicks off on it's own

then i notice the speedometer bouncin a lil

gets worse

starts dropping down considerably...
engine revs a lil higher...

finally get off at my exit
doesn't wanna shift back into third gear

finally does
get stopped at a light
feather the gas pedal to get it to shift into third again...
then another light
won't go into third

limp 20miles to mechanic's garage in 2nd at about 25mph on the shoulder with flashers on

now i've had this happen before in a '99Chrysler 300M
that turned out to be a speed control sensor...

but this time there were no error codes in the Tahoe's computer

think it's a gear inside the transmission
mechanic said he could just get his pinky finger on it and that it "felt loose"

but he doesn't wanna tear through the back of the transmission, removing the transfer case, some bearing and all that to get to this thing... only to have it turn out to be something else...

didn't feel comfortable doing it
not exactly a transmission guy

i live in the sticks
may as well take it to the Chevy dealer

unless someone can confirm that it was just extremely likely to be this speedometer gear inside the transmission... crap... can't remember what he called it...
started with an "R" + "gear"
that is likely spinnin on the shaft, giving a false reading to the computer telling the transmission when to shift...

does that make sense?

ohyeah
it'll drive perfectly now...

shifts through all the gears

so we're THINKING that that speedometer gear got hot from the "long" trip and started it to spin on the shaft...
or something.
..
~

[2000CAYukon]

A scan tool will tell you if the speed sensor is wrong or not working (which it does sound like this is the problem) when the problem occurs. Then is makes sense to look at the sensor and gear.

You need to find a shop that has the right equipment to diagnose the problem.

//2000CAYukon

[arneybass]

My 1997 did the same thing about 2000 miles ago and i replaced the speed sensor at the rear of the transfer case and didn't have any more problems with it till today!!! Started the same thing going to work this morning and this afternoon it won't come out of second gear. when it does it does some crazy shifting and the speedo won't work. i checked the reluctor gear and the sensor and they both look good!! so i bought the best scanner they sell at advance and it said the input speed sensor A is bad. does anyone know where this one is??? I replaced the one at the rear of the transfer case and i don't see another one?? Thanks for your help.OH and i think these are good trannies!!! I have 350,000 on it and the motor with no smoke and no slipping or lots of clutch dust in the pan when i service it. And it has pulled a boat or a car trailer 90% of it's life!!! I'm impressed with mobil one oil!!! Thanks for any help on this subject you can give!!!!