i replaced the sensor on the tailshaft of the transfer case, but its still acting wierd. almost like when the engine is above 2,000 rpm the speedo goes nuts. its fine until you want to get on the highway. anything over 55 the speedo goes crazy and shifts all messed up. where do i go from here? what do i do? im at a loss on this one.

 

Depending on what 4wd system you have, there could be two different speed sensors in the rear output housing on the transfer case. Being an Envoy trimmed Jimmy means that you likely have the NV236 transfer case which would have two speed sensors in the rear output.

You can test the sensors first for resistance which should be 1300-2700 ohms. If it isn't replace the sensor. If it is, then test the output while spinning the rear driveshaft. It should be >0.5V-AC.

 

There's 4 buttons on the dash, auto 4wd, 2H 4H 4L. Im sick of this thing breakin down on me. It's got 186k I replaced the. Engine, tranny and rear axel. I'm into it for way too much money and I'd take a killin if I sold it. So I have to fix it. Also there's a vibration, comes and goes around 75-80. I had all 4 tires balanced. U joints are good. I can't figure out what else it could be. The vibration is in the seat, not the steering wheel.