Is there a maximum number of t5008 you can autofill from CRA website? Have over 350, wondering if this is why I keep getting stuck here.

Yes, TurboTax has a maximum of 30- T5008 slips. As an alternative you can combine the amount from each box - make sure they are separated if different currencies. So therefore you would add all of your boxes 20 together and so on.  

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