That is done under the Farm/Business Assets (depending on if you use Schedule F or C) section in TurboTax Home and Business (see images). TurboTax will walk you through setting up the truck and calculating the depreciation to expense. When you indicate that this is a new asset, you will be given other depreciation options.
If you sell a vehicle that has been depreciating for 5+ years, then any gain on the sale of that vehicle will be increased by whatever depreciation expense was claimed while it was in service.
(If you had a loss on the sale, it would have been reduced by whatever depreciation expense was claimed while it was in service).
Gain (loss) on the sale = Gross Proceeds from Sale minus Cost (what you paid for it) plus Accumulated Depreciation.
I'm assuming you own a business and the asset has been depreciated through a Sch F or Sch C or some other business.
Because you use it for business the sale is reported on the Form 4797. The best thing to do is buy a replacement car/truck and then treat it as a like kind exchange. Which is reported on the Form 8824. There you will have to run through a computation on a worksheet which will give you the basis (for depreciation purposes) of the replacement vehicle. 2020 Instructions for Form 8824 (irs.gov)