Transmission not shifting past first

[2vVic]

I have a 2000 mustang gt (auto) it just hit 110k miles, the transmission won’t shift past first. But reverse works fine. When I manually shift it 1st to 2nd and the put it in drive it shifts but very sluggish. I checked the oil and it’s full and red. When I have it in drive it won’t shift and the rpms just climb and it basically goes in nuetral till I let go of throttle and it goes back to 1k-1.5k rpms then the car feels like it’s back in drive. I’ve never had this problem before and the day before it was working fine and when I turned it on and drove it it did that.

 

[01yellercobra]

I'm assuming no codes or lights.

I would drop the pan and look at the filter. You might get lucky and only need a new filter. I wouldn't do a full flush though. But it seems when these trans act up something inside is amiss.