Ok so I just had the head gaskets changed in my a8 and the tranny is acting up slightly which i knew about but the mechanic said he saw the rubber on an engine mount was worn badly so he removed the rubber only and the spark plug connecters are cracking slightly i guess so it could possibly start missing at anytime. the problem is that the car shakes violently after its going down the road and only at low rpms when i press the gas. example: I take off gently and get to about 40-60mph put it in 4th or 5th gear (tiptronic automanual tranny) and when the rpms are just below 2000 the more i press the gas without shifting the harder it shakes, when i coast its smooth as can be again or if i shift down and raise the rpms its fine again. could this be teh engine mounts missing rubber? thats my best guess. ive been told its maybe the tranny but thats not the case im sure by the way it feels it cant just be the tranny doing that out of nowhere. maybe the timing?

I think you've answered your own question. It's not a timing issue because it would get progressively worse at high rpm. It's unlikely to be the transmission, because it would be more likely to cause knocking or grinding noises. So, the only reasons left are, wrong tyre pressures or loose engine mounts - you've already mentioned that the mechanic removed the rubber and I am going to assume that he replaced them wrongly. If he did not replace the rubber then there's the problem right there, and it was crazy not to do it.

Low frequency vibration suggests that it's the engine mounts, but do check the tyres and tracking of the wheels too.

It sounds like the tranny mounts. Cars can have harmonics that cause rattles at different speeds and rpms. It sounds like you found that harmonic below 2000rpm at speed. The vibrations from the tires, the road and the engine combine to cause shaking at certain speeds. Replace the mount before anything else.