I have a 2000 a4 SS with 119k miles on it, slp lid, headers, ory, and egr delete are only mods. Picked it up back in November and ran good ever since. Today I was cruising down the road had it in Drive and had to stop for a truck to turn. After the truck turned I took off and the transmission shifted hard from 1-2, after second it wouldn't shift into 3rd. All it would do is rev and not accelerate. The cel is on but only for a o2 sensor which I've noticed it was acting up for the past week. It shifts extremely hard and won't go into 3rd or overdrive. I changed the transmission fluid back in December, and checked the fluid when it started acting up and the level was good. What could be the problem?

Thanks,
Joe

 

The "all it would do is rev" in 3rd gear is a good indicator that the 3/4 clutch is worn out. The PCM probably detected the slippage and maxed out line pressure to reduce slippage; this also gives you a very hard 1-2 shift.
Did you recently scan for codes?
There are probably 100+ threads here of "slips in 3rd" or "no 3rd gear". Nearly all turn out to be the notoriously weak 3/4 clutch. Very occasionally, it is just bad shift solenoids. A full list of codes can narrow that down.

 

Checked codes tonight, only one that showed up was the o2 sensor.

 

Check this out: