Have you tried to find out why your team has become stagnant?
Are the current tasks outside of your team’s expertise and experience? In that case, it might help to get outside help. You could consider getting someone helping the team temporarily as an interim or consultant, or recruit people with the required skills. This way your team could get knowledge transfer and know-how in the process.
Outsourcing the entire project may sound like an easy way out but it has its downsides, too. If your need is a one-time thing then this does not matter too much. Yet, it’s important to know what to buy and how in order to achieve the desired results.
I would also consider how crucial / critical (i.e. strategic) the tasks are for your business. Are they at the core of your value creation and benefits that your customers appreciate? By outsourcing you will lose much of the (quality) control and also the continuous learning process. Also, it’s harder to pick up weak signals from your partners.