Running flat spots/no power

[Jas_saxo]

Got a custom fitted catback last friday (longlife zaust)
Sounds amazing and felt some power gains
But yesterday the car started running flat spots in every gear an cant put the power down!!!
Feels like the zaust is for some reason restricting power
But then after 10-15 mins driving its fine again!!
Any help anyone???
Cheers!

[stevo67]

Any blows in the exhaust joins?

[Jas_saxo]

Goin back to where i had it done today to get them to look it over

[Jas_saxo]

all seals good and tight and cat is mint perfect nothing wrong there
they suggested its the lambda sensa
any one??