same thing happened to me no 3rd or 4th no codes no lights just 1 and 2 strong too i did punch it to 80+ i tried everything but the first step is pull the pan and look at the condition of the fluid if it has clutch debri gray looking or silver metal like material in the fluid then u lost 3 and 4th clutch pack very common on chevys' I got a tranny from everdrive used but no core charge so it gets u going while u get the money to put a monster in a box kit on the old one and drive another 200k at 80+hahaha.