Hey everyone! I've been searching for an answer to this problem for about a week now, and can't seem to figure it out. I'm pretty new to working with my car, but I'm learning as best I can (we all have to start somewhere, right?).

So! Basically, I have an 04 3.9 v6 with an automatic transmission which has recently been acting up: the speedometer reads 50-70mph even when in park, and jumps around in all other gears. It shifts fine at highway speeds, but if stopped at a light, it acts as if it's skipping the lower gears when I try to accelerate (it eventually catches up and slams into gear somewhere around where I think third should be). Also, whenever I stop at a light, I can hear a short "whooshing" sound from the passenger side of the engine bay. Additional symptoms are that the Overdrive off light keeps flashing (In my research, this indicates a transmission code has been stored... but I haven't been able to pull any), and the odometer ticks up.

I replaced the VSS because I figured that would be a good, easy place to start. It seemed to make things better for about a day... then I was right back to where I started.
I would love to have some help on this! I'll apologize in advance for how inexperienced I might sound on this lol

 

I would have said start with the VSS but you already did that. The speedo is full electric on your year so its that, the wiring to or the cluster itself.

 

Just went through this with my truck, and had to have the transmission rebuilt. Had the same symptoms as you are describing, loss of gears and the overdrive light blinking. I found the overdrive light blinking means it is a transmission slippage fault. I would have to say time to have the transmission repaired.