Extremely big haul, right? Doubtful (5-4)

I believe the answer is:

ultra-high

'extremely big' is the definition.
(very high or big)

'haul right? doubtful' is the wordplay.
'doubtful' indicates an anagram.
'haul'+'right'='haulright'
'haulright' with letters rearranged gives 'ULTRA-HIGH'.

I've seen this clue in The Independent.

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