Vauxhall Vivaro lack of power

My vivaro start fine but when I go to pull away I have to give it some high revs to move or it doesn't want to move if I start to go up a hill I loose power and always have to drop it down a gear it's fine when the turbo kicks in but if the revs are not high enough it really struggles could this just be a problem with air flow or is there more to it also before this went like this sometimes when I was driven when I put my foot on the clutch and released the accelerator the rev stay up a few seconds before dropping to idle not sure if this due to the same thing or not. Cheers for any help in advance