Tranny problem
I will assume your tranny is a 4R70W or 4R70E...in any case, one or more of the shift accumulator springs may have broken. You don't say which shift is so abrupt, I'll say it's 1-2, but it doesn't really matter. The pan must be pulled to access the accumulator covers and each one must be removed and the accumulator assembly inspected for broken springs or worn out piston seals.






