I have a 98 chevy k series truck, V6, 1/2 ton 2 wheel drive, automatic transmission with 271000 kms. The speedo and tach does not work, and when you drive the vehicle down the road it is sluggish to start accelerate because it will not shift down to 1st. eventually when you do get going it will drive properly aside from the fact that it will not shift. Sometimes the speedo and tach will work but is very eratic. I have taken the transmission pan off to see if there are any parts and to see how the oil is and there was nothing to find. i have a few codes that have come up that include shifter A and B, shift control module. I have been told to check wire connections which I have yet to try. Also checking the speed sensor on the tailshaft of the transmission was also suggested which I have to try yet.

radamk; The transmission shifting depends on the VSS (vehicle speed sensor) input. Take the suggestions you've been given.
Loren
SW WA

I replaced the speed sensor which did improve my situation. But it is still eratic where I can drive for a little ways and the tach and speedo wont work right away but when they kick in they work fine but it still does not shift properly but I can shift the gears manually all except overdrive which seems like it is never there lately