Losing power on highway

Piaggio porter 07 is losing power on the highway.
It is running fine, then feels like you have taken your foot off the accelerator but you haven't. If you put the clutch in and let it coast for a few seconds then put it back in gear it works like normal again....
Any ideas about this?
Thanks guys

I was doing some reading in here and it seems this could be caused by a speedo issue? We know our cable is toast...

Yes certainly the speedo cable is the problem. It will probably run ok up to about 40mph but after that it will cut out and you will have to sit at the roadside like a lemon until the ECU resets itself.
It happened to me 22 times on the way back from Berwick on Tweed to the Island. I got to Watford before I found that sitting at 40 to 45 was the answer to getting home trouble free.

Nice... Thanks for the confirmation!
Ours has cut out countless times so far,
We are driving from manc to Dundee area,
Luckily our ECU resets pretty much as soon
As you put the clutch in. So far we've been able to keep rolling.

..... So far.

Thanks for the help!!

Keep it at a steady 45 and you should be OK if my experience was anything to go by.

But with mine I had to sit there for up to five minutes just ticking over before the accelerator pedal would respond.