It can't be the breaks Chris it has to be engine side.
The slowing down you could put to brakes but it's not that kind of slowing.
It's more like what I had with an old car when the piston seized, like being in a manual in gear and the engine dies, it's that kind of slowing up, then the rev clock climbs 1 digit and it carries on fine.
Also if you accelerate reasonably firm up to about 40 and then ease of a touch you can get a physical lurch (lick dabbing the break pedal firmly) and a kind of miss fire down the exhaust. At the point when it lurches it goes quiet, it's like instant fuel cut.