Bad Fuel Injectors, Nozzles or Mexican Fuel??

People here say that the nozzles should be replaced at the 100,000 mi mark. I'm sure the injectors themselves are fine.

Is the idle rough? Is it like its pinging or knocking? With that many miles yes, the nozzles need to be replaced. Its a gradual thing though, and you may have another problem.
You can get the nozzles replaced pretty easily. As long as the place can replace injectors and has a vice and 15mm deep socket you're set.

Techron?

with a sudden power loss, I would look for a vacuum line or some such.

Thanks for your responses.

The idle may be a little rough, but not anything very noticeable. I am wondering if the MAF might be a possibility here. I changed it 4K ago. Would the check engine light go on with an MAF issue? What kind of vacuum issue might I be dealing with.

So it sounds like the power loss is most pronounced under a load, while going uphill.

How long has it been since you replaced the fuel filter?
When was the intake last cleaned?

I have not heard of anyone using Techron on TDIs. If you can get your hands on some, try using Diesel Purge. There is a recent How To:
http://forums.tdiclub.com/showthread.php?t=87948&highlight=Diesel+Purge+how+to

Techron is not the best choice for a diesel.

With a sudden loss of power and black smoke, I would be looking at the large black hose that connects to the intake manifold. It probably has a split in it. Classic symptoms.

With a 98 TDI, I would replace all the vacuum hoses, preferably with silicone. That includes the hose INSIDE the ECU. They're old and hardened. Don't check them, change them.