1999 Land Rover Discovery 2 Runs Rough

Engine Performance problem
1999 Land Rover Discovery 2 V8 Four Wheel Drive Automatic

Starts fine - idles fine - out of gear I can increase the RPM and it runs smooth.

In gear at about 25 mph and up - under load - (acceleration)- we get a vibration almost like a misfire.
If I let off the gas it stops.
Vehicle will coast with no vibration - only vibrates on acceleration.

Engine light came on -
We got codes that the forward Oxy sensors were slow to respond.
We have had also had codes for #3 and #5 misfires and now #6 and #8.

We have replaced plugs, tested wires, replaced forward oxygen sensors.

After replacing Sensors we still have vibration on acceleration but have been driving it for 5 days approx 300 miles and NO engine light. But still have vibration.