Discovery 2 V8. Sluggish performance

My 2001 V8 ES was taken into my local service agent yesterday for routine service. They informed me later that they had noticed that the car was a little sluggish (I had not noticed!) and found that when hooked up to a machine (?) the car was recording a drop off when revved and the machine was recording too much oxygen as the cars engine was revved.
The garage has baffled me with so much technical information, I am totally confused!
I have no idea what they are talking about and hoped that someone may be able to explain to me in terms I could understand, and possibly share any similar experiences with me.
The car has covered 70k miles and has been serviced every 6k miles.
Thank you!
Dan

Did the garage print off any live data readings or fault codes,without more actual data it will be difficult to offer any real help.

I know that on the v8 the followers and cam do wear over time resulting in a slow and un noticable decrease in performance.

Thank you, they did mention two fault codes, I will ask them what they were and post them.

Thanks for your reply, very much appreciated.
Dan