Tax on Gain from lease transfer of non-depreciated business equipment

I'm an independent trucker and leased my truck in October 2019.   I put $14,000 down and have made 33 monthly payments with 17 payments remaining in the term.  I'm transferring the lease to someone who will pay me more than the remaining balance of the lease.  How do I calculate the basis and gain, and how do I report this to the IRS?   IRS Form 4797 applies specifically to real estate and depreciable assets, but as my lease is an 'Operating Lease', I deducted the payments like a rental and did not depreciate the truck, so I'm not sure how and where to report this.