I purchased a truck in Aug 2021, used it personally, and then became a Sole Proprietor in March 2022. Can I claim my truck as a DIEP?

No. You can’t claim your truck as DIEP, as you already owned it. You can’t claim DIEP on an asset that you have already been using for another purpose.

Could it qualify for Accelerated Investment Incentive or do the same rules apply?

Thank you in advance!

Yes, the same rule applies for the Accelerated Investment Incentive.