Violent Trany Shake in 3rd Gear on A4

First of all, the trany has been modified. I don't know if it is internally modified or if the Line Pressures were tuned through the PCM, but it has one hell of a firm shift from 1-2 and a descent shift from 2-3.

Question is... When driving around in 1st everything is smooth. 2nd, smooth. 3rd, the whole damn car starts to shake violently. Shifts into OD, smooth.

Any Ideas? Car has 60,000 on it.

Driveshaft out of balance maybe?

I thought about that, but once it shifts out of 3rd it's ok. I would think if its the driveshaft that it would get worse as speed increases.

I had a U joint go out in my driveshaft that caused a mild vibration in 3rd gear only. It was the rear U joint and it had a dead spot in it. It felt like it had a detent.

Weird...Ok, I'll check it out then.

I thought if it were anything past the trany that it would do it all the time.

Thanks for the info.