2004 Kia Sedona Severe vibration at 45mph to 55mph

My '04 Kia Sedona has developed a severe vibration when accelerating through 45-55/60 mph. Once you hit 60mph no vibration. It also vibrates at very low speed when turning hard right.The vibration is coming from the front nearside. Wheels have been balanced and rebalanced, 4 wheel alignment done and redone. Suspension torsion bar bushes replaced, front nearside driveshaft replaced. Suspension checked and rechecked. Auto gearbox specialist roadtested and said gearbox can't be causing the vibration. Kia dealer out of ideas. Very experienced mechanic losing his hair and sanity over this problem.
First noticed at same time as rear nearside wheel bearing collapsed, replaced but vibration continues on and on..... (probably just co-incidence). Any ideas greatly appreciated.