Ruking, your originally posted trip descended over 4000 feet of elevation! Completely irrelevant data point. This is not helpful, as presumably the OP is not asking us "how good can the mileage be at high speeds, when driving downhill for an entire tank, with a tailwind and magic fairy dust in the fuel tank?"

You are not posting normal fuel economy numbers. We have a few geezers who drive at 50mph to pull off their great #s. And a few newbs who don't know how to properly evaluate fuel economy. But then there is you, repeatedly claiming mileage feats that no one else can accomplish. So yeah, either your TDI is magical, or you aren't being completely truthful with yourself and your mpg calculations.

I am an engineer... dedicated to using hard data to find truth. Not interested in exaggeration, manipulation of data, or, on the other hand, knocking people's results when I have no reason to doubt them. But I do have reason to doubt your #s here. Actually, to be honest, an odometer error makes sense for your car, since you also claim 112,000 miles from a set of goodyear tires.

Let's take another look at this situation objectively:

Have you seen an understood the BSFC map for the ALH TDI engine? Search for and read the BSFC thread if not. Below is a calculation of the load required to push a stock Mk4 Jetta down the road in top gear. Let's run some simple numbers for your stated speed of 90 mph.

A fairly basic calculation tells us we need ~42 BHP (31.5 kW) to sustain 90 mph. With stock gearing and tires, this is ~3100rpm, which means we are requesting ~71.6 lbf-ft (97 N-m) of torque. So, that puts our engine efficiency at around 245 g/kW-hr. 245 grams * 31.5 kW means you are burning 7.72 Kg (17 lbs) of fuel per hour at this speed. Divide by the density of diesel fuel (6.9 lbs/gal) and you can see we are burning 2.45 gals/hr. At 90 mph, this is 37 mpg AT BEST. And you claim 50 in the rain? Ridiculous.