1999 Jetta Wolfsburg

Alright I bought my car and had the oil changed, it had documented oil changes, gear box fluid changes, tune ups, and the thing had only 75,000 miles. Now the hunk of metal doesn't rev past 3,000 rpm, and has absolutely no power. I had to have it towed over an hour and a half away from my house. I had all electrical components of the engine replace, and all parts dealing with the fuel replaced. The mechanics and dealership can't figure out what's wrong. Any ideas would be great i need to have the thing running before i can sell it.