1993 bonneville sse 3.8 non supercharged 104,000...when i shift to drive, reverse, or overdrive while the engine is cold it will slip and act like it is in nutrual but will still slowly roll....but if i put it into #1 it will slip slowly roll foward then engage after about 4-6 seconds..i replaced the tranny filter and fluid with no help...i recently replaced the upper manifold gaskets when the problem started....no trouble codes and the car shifts well durring normal driving, runs well, and will engage into drive while the car is still warm...any help will be much appreicated..this is my only way to work and back..the problem has been progressively getting worse over the last 6,000 miles

Plan on a trans overhaul.