You need to completely take the transmission apart. Use the book that Wyreth is sending you or use an ATSG service book for the C6. Once you have every last nut bolt and screw out of the transmission DISASSEMBLE EVERYTHING, clean everything including the case clean enough to eat off of with solvent. Once everthing is clean inspect everything for wear, Front pump gears, planetarys and every moving part. Use clean newspaper to set everything on once it is clean, only use cleaning solvent and blow dry, NO SHOP TOWELS! completely disassemble the valve body also keeping everything in order of each bore it came out of. Then buy your parts. You will need a kit preferably with a fiber pan gasket, A shift kit, add on cooler and external filter are also good for longevity, Deep aluminum pan is also a good addition. You may need additional parts besides what is in the basic kit such as bushings, thrust washers, band apply piston, intermediate band-can be any material dont spend extra for a supposed hi performance band. Then follow the book directions to reassemble transmission. Replace the torque converter as well, a stock one will work but a tighter one will work better if you tow a lot of heavy loads. PM me if you have any questions and I can help you through it and I can provide you with the kit and any parts you need for it.