Thanks for your reply.
Yes the post motor filter and cover were replaced.
As stated, the DC33 picks up ok and you can see visible lines on the carpet as you clean each section but, unlike the DC33 with the previous motor and, every other Dyson that we have owned (DC01, DC02 and two DC07 (one carpet only and the other multifloor), the suction was that good that when new an also when the filters were periodically cleaned, dust collector emptied, you could see the carpet being sucked up to the bottom of the cleaner as you went over it - with the replacement motor, that does not happen.
I'm getting suction from both the cleaner head and the wand but, for the reasons just given, I know that the suction from cleaner head is good but not as good as it was before; with regard to the wand, again the suction is good but unlike the cleaner head sucting up the carpet, I have no way of checking if the suction is the same as it was.
Also, when the DC33 is powered up and the handled pulled down to vacuum the carpets, the brush bar does spin and, in that position, when you turn the floor control back to 'floor', the brush bar stops and I think that this is normal?
With reference to the 'clutch', I have no idea if it was switched to 'off' but, as stated above, the brush bar is spinning when cleaning the carpets.
One last thing, I've noticed that, at the base of the dust collector, there is a lot of movement and the rubber seal on left hand side (as you look at the front) does not appear to be sealing properly against the bin and every so often we get dust settling behind the dust collector on the body from the top of the bin and down to the bottom so, this to me means that when assembled with all seals in place, the DC33 is not airtight.