Why does a fiat brava sx80 shudder violently when moving off uphill This car had a new clutch less than 4000 miles ago?

if it had the full 3 part clutch fitted (friction plate, pressure plate and release bearing) then it could be an oil leak from the crank rear main seal ( the seal encircling the crankshaft behind the flywheel) when oil leaks into the bellhousing centrifugal force throws the oil around the bellhousing often finding its way onto the friction plate causing a grip and slip feeling (shudder), alternatively it could be a fault with the ignition electrics breaking down under load ( such as heavy accelaration or hill start) look at the spark plugs, ignition leads incl coil lead or the coil itself.