Between regenerative braking and the fact that EVs don't need transmissions (which stop and go traffic is especially hard on), it does seem like a no brainer.
So far, data shows that well-made EVs have lower maintenance and repair costs than legacy vehicles in similar categories. There are definitely some fairly unreliable EVs—early leafs with horrible batteries (early technology), and exploding chevy bolts (GM...you tell me), but that isn't true for the latest or high end vehicles. Also, the USPS is self-insured (and therefore insurance costs are irrelevant), and chip shortages would really only impact the steady delivery of vehicles and (to a lesser extent) service parts.