Sorry you'd been having trouble with you car. Long post here - hope something helps ya.
BobnOH is right, with the correct TB special tools you can start with no belt at all (everything off timing) and it will all come together correctly timed. The IP pulley bolts are loosened at one point for a "correct" TB install to relief the stress and thats why it requires a VCDS to check and tweak the timing after its put back together.
Unless they have worked on this particular model engine before or you paid them really good I doubt they have ALH specific TB tools (IP locking pin and the cam locking tool are most important). Just the delay of the job waiting for tools in the mail would be a reason to try and skip them even if they were free. Most mechanics don't think you really need them - some gas engines use special tools also but you rarely actually need them. Getting them to fix it right or getting your money back is probably never going to happen sorry to say. If it was me I'd only be trying for the money back. For the same reason I don't ask for food to be remade at a restaurant, unless they really take pride in their work if they messed up the first time are they really going to do better the second time, especially pissed because your making them do yet more work...
If your still not sure if your brakes are dragging or not, go for a normal drive and try not to stop too much then pull it over. Go feel each wheel for heat, they should only be a little warm depending on how much stopping you did. Don't touch the rotor directly you might get burned pretty bad. Or if you have access to a IR temp gun use that. No correct temp lots of variables, but one side shouldn't be much hotter then the other.
As others mentioned fuel leaks at IP or return lines on the injectors - fuel filter and air filter although they would have to be pretty old for that mpg.
But if this (mpg drop) happened suddenly after your TB job that is your primary suspect. Without the special tools the cam timing could also be off even if the IP is set perfect in VCDS.. I'm not sure of anything you can read with the VCDS that will show the cam timing. This can be checked physically by removing the vac pump and using the transmission hole to set the crank in position and checking that the end of the cam is very close to where it should be.
Not in the business of fixing other peoples cars, but I am in the Chicago area and have all the special tools if you give up others. Hate to see a alh get destroyed. If you want to get in touch send me a PM.
Personally I don't trust anyone even the dealer so I do my own work -- I don't even let someone drive the car into a garage to put tires on, I bring them in my trunk and swap them at home. I've had too many bad experiences to trust anyone else (a tire installer damaged my transmission, and not in a big enough way for a insurance claim so i had to live with it), its worth my extra hassle to not have potential problems. Its worth the walk to park in the back of the lot etc. People don't give a SH*T about their brand new car, so putting a small dent in your old tdi with their door doesn't even mean anything to them. -- Same reason mechanics dont fix things right, most people dont care and want cheap.
IMO if you need to pay for work, its worth paying more (or going out of your way to the right person) to not have potential problems. I would only ever recommend someone on the guru list to anyone I know, at least for the engine stuff on a TDI. I mean how many mechanics even use a torque wrench, next to none is the answer if you didn't know - its simple economics - time is money and being anal takes more time.
Sorry if I am coming off preachy just my opinions take it or leave it.
Edit- Maybe all your over-fueling could have loaded/clogged the cat up too much? how is performance?
