Shuddering whilst accelerating or climbing hill

When I accelerate or start driving up an incline or slight hill on the open road, the vehicle shudders and vibrates. The engine seems to be running fine. One repair shop I took it to said it is the injector and all need to be replaced but cant guarantee that it is the problem. Wanted a lot of money to "experiment" on vehicle. Another repair shop said it was in the gear box somewhere but will never cause damage or get worse. If the vehicle was supposed to run like this it would have from new. It definitely is not right. When I had a Land Rover Defender and mileage was also around same km's it did a similar thing and it was the "spline" (may be the wrong word or description, sorry but I am not a mechanic) from the drive shaft into the rear differential that needed replacing (very low cost) and it was like new. This is front wheel drive though and I have not got a clue where to start looking. I do not trust agents as at 105,000 kms I noticed water in the oil and I was told by the VW agent to replace my motor! At a higher cost than I bought the vehicle from them as a demo model. A mechanic in a small private repair shop did not even look at the vehicle and told me that the water pump was leaking water on the bearing and into the sump. It cost me $3,000.00 to fix it. Has run up to now with no water leaks. So there, do not believe your agents they love money and cannot repair anything, can only guess and charge a you a fortune. If anybody can assist I would appreciate it.