General question 4T65E and transmission fluid

I hope this is the right drive-train forum--Can someone explain to me the properties of Dexron lll when cold, and when hot. EX- What happens as it heats up in trans.? Does it get thicker or thinner as it heats up to operating temp. Just trying to understand the working in the 4T65E during warm up. Reason for asking, 2005 Impala 3.4 shifts good and grabs like it should (slight hard shift) for about 30-60 min after cold start, but after warm up you have to manually shift till you feel it grab without torque then it'll go without slip, but ya gotta let it grab first. I realize this Mdl. trans. has had all kinds of issues, but I'm trying to understand this after the fluid gets hot. I also realize the trans. probably needs work, just trying to understand whats going on with warmer fluid vs colder fluid as the trans. parts also heat up. Thanks.