Not sure wich speed sensor to replace on my 97 town and country.speedometor very erradic and tranny not shifting correctly

that seems like the filter in the tranny pan is packed up in gunk.
as in HOT ATF flows better past junk there.
cold not.

The speed sensor would be a likely suspect.
It takes the place of the speedo cable going from the transmission to the speedometer.

97 c1500 or k1500,. not told. just 1/2 ton sure. K1500 is 4wd got that?
the 4wd sensors are not the same. ok? no engine told either, guess 4.3L only
4L60-E; 4 speed Automatic trans. or 4L80e
that is and E box, electronically TCM shifted.
and the speed sensors must all work!! must !
it it can not shift correctly.
that is a fact.
you replaced 1 but never say the speedo was fixed, yes the speedo matters
OD is 4th gear,
the TCM can be scanned, why not do that?
stuck in 2nd gear is common for TRANNY LIMPHOME
it does that when sensors or solenoids go bad.
making car safe to drive to a shop only that is all limphome means just that.
beats a 100% dead car no? for sure.

sensors all 2, input speed and outputs speed, and if 4wd OSS is on the rear of 4wd transfer care, moved, for 4wd.
solenoids not bad in box. 1>2 and 2>3 shift and 3<4 shift.
scan the TCM.

the ECM on the car 4.3L runs the Tranny (TCM logic) 12 connection.
so not scanning the ECM OBD2 port ,you fully miss the boat and it sailed
the good ship of facts gone. DTC errors for sure missed.

we can here,
your van is going into "limp mode"
when the computer does not get a correct signal from transmission it will not shift because it doesn't know your speed or engine RPM,
Three sensors on the transmission will trip it into limp mode,
1= output sensor,
2=input sensor,
3=speed sensor,
if you have it checked and get a "P0000" type code
it will tell you which one

Try output sensor for the transmission (it is similar to a vehicle speed sensor), these can control the speedo and shifting. Not sure if it does anything to the rpm guage, but very possible.

Yes, the car will probably shift harder (if it has an automatic transmission) and it won't shift correctly when you try to accelerate at speeds over 30 MPH (it will downshift too many gears).

The "S" light flashing means the speed sensor went out. Is an easy fix. I got mine for less than $40 and it was not hard to install. As for the gears going in too slow, I dont know. Good luck.

Check the speed sensor on the tranny cause if the speedometer is not working the tranny will not shift.The computer will not recognize that the transmission is in motion so will not shift.

well i would try replaceing that sensor first it is a speed sensor and it has a lot to do with the shifting of that tranny if it dose not work yea with what you have exsplained it is probly time for a tranny but this fix is worth a try thanks kdc744

If you were to take the solenoid pack apart you would find a bad connection on that solenoid. You sill need a new pack installed.