I want to sue a Mechanic shop for saling my truck?

In 09 had a trucking company took one of my units for engine oil leak repairs engine was disassembled it costed me $10000 for the problem to be solved took cylinder head for mechining the when the job was complete went to pick up my Truck and the engine was still leaking oil ,the job was redone after i complained never picked up my truck ,the mechanic said the cylindr head was not mechined properly the engine the engine was disassembled again te Cylinder head rechecked and t was proven to be ok tey reassembled the engine and the leak was still present and i was chared anoter $1200 for labour with the initial problem not solved ,i lost Truckig my contract due to failer to bring te truck to work on time ,could not pay the bill ,the Mechanic shop started billing me for storage finally they said the bill need t be paid so truck had to be sold ,i agreed to sale the Truck at a $15 -$18k failure to that i was gon to pay the bill and retrive my unit and suffer the loses ,the manager was willing o take the truck to an Action but i had to sign a bill of sale in order for him to sale the truck on my behalf since i had moved out of town at that time bil of sale was drafted and no amount pu in there and later he told me he had sold my truck for $5000 what should i do?