VW Problem Holding Speed on Hills - BOTH CARS Doing It

We own two diesel VWs - one is a 2001 Beetle, and the other is a 1999 Jetta. Over the winter, the Beetle began experiencing problems driving over the Oregon Coast Range (app. 1600 feet). The car gets to a point of the incline where it will not accelerate, and will not achieve speed above 40 MPH. The problem did not occur anywhere else. Went to the dealership 3 times for fuel filter replacement, carbon cleanout, etc., and they can’t fix it. Also, they can’t duplicate the problem because it only occurs on the Range, which is about 1.5 hours away from the dealership. The problem on the Beetle has improved, but still occurs for about 30 seconds each trip. NOW, the Jetta is doing it too. Yesterday, for about 20 minutes we had no acceleration on the Range, and could not drive above 35 MPH. In both cases, you can rev the engine, but its like the transmission doesn’t respond and kick into the next gear. The Beetle is automatic, and the Jetta is manual. Both use biodiesel and regular diesle intermittently. HELP!

The bio-diesel thing is common between both cars.Has the dealer made any comments about the use of bio-diesel?

I believe VW only recommends 5-20% bio on most of their diesel cars. That said, it appears quire a few users don’t have problems with higher ratios.

I wonder if the turbo is having problems?

Only that the rubber hoses/gaskets, etc. might suffer deterioration. That happened to me last fall when my car started leaking fuel all over the place. the Jetta went in earlier this week and got a new air sensor that controls how much air/fuel gets to the engine. We’ll see if that helps - will travel over the mountains again next Saturday and will know whether it’s fixed or not.