The new provider of non-emergency NHS transport services in Sussex has blamed "mobilisation challenges" for poor punctuality in its first three months.
South Central Ambulance Service (SCAS) took over from Coperforma, which lost its contract over long delays and issues with sub-contractors, in April.
Data obtained by BBC Sussex shows SCAS had so far missed its targets on every measure of punctuality.
SCAS said it had been "mobilising a very large service at short notice".
Deputy chief executive James Underhay said a consequence was "the timeliness of pick-up and delivery of patients".
He said the first three months of the service had still been better than the first three months for the same period last year.
Mr Underhay said the service was seeing about 31% more patients "than we were led to believe when we were going through the planning stages".
BBC Sussex political reporter Ben Weisz said SCAS had improved month by month but there were still some measures - particularly the proportion of patients waiting longer than an hour after a planned discharge from hospital - where performance remained worse than it was under Coperforma in early 2017.
The NHS High Weald Lewes Havens Clinical Commissioning Group, which hired SCAS, said despite the poor start it was pleased with the new provider.
Dr Sarah Richards, chief of clinical quality and performance, said: "Obviously nothing is ever perfect and we've strived to continue working with SCAS to improve things further but generally over the last three months we've seen a great improvement in the data, the performance and the quality of the service."