You CAN sell the gear before the commitment is up. You own it now. Deactivate all receivers, except for one. Keep the minimum programming package for the one receiver. Sell the deactivated receivers, and any switches/lnb's.
I did forget about the HD Pack commitment. (I was able to get out of mine as a result of complaining about the problems with the 811.) The HD commitment is pro-rated, so you will have to pay the remaining months. Just do it in advance, along with the AT60 fees.
Just remember to deactivate that last receiver, and cxl the account, at the end of the commitment, or they'll keep charging you.
(The above is based on you not being a DHP or DHA customer, and not having any additional contract obligations with a retail dealer or other third party in addition to Dish.)