Disco 2 V8 Misfires, poor running and o2 sensors

Hi all,

Trying to narrow down and fix this myself before taking it to a garage hope someone can point me in the right direction.
A few weeks ago felt like I lost power while driving. when cold losts of misfires pulling away, improves slighty when warm but a real struggle to get to 60mph.
Lasted for a week then went away completly. Now its back.
Had codes for catalyst damaging misfires, P0150 and P0130.
Ive replaced both o2 sensors, cleaned the connectors, no change in problem but codes are now P0155 and P0135.
No change with MAF unplugged.
new coil packs,plugs and leads 1 year ago.

thanks for any advice or suggestions I can try.

Hopefully your O2 sensors are NTK, Walker or Denso and not Bosch.
Bosch O2 sensors are problematic right out the box brand new.

Just got britpart ones from John craddocks, I'm starting to think some form of gasket either head or manifold.