when my cavalier rpms jumped up and down, mainly in gear, the iac was gummed up, problem went away after cleaning it, if tranny is slipping that'* a different issue. I'm referring to engine racing for unknown reason.

The trans doesn't slip in anything else though, only initially into drive. I will put in gear and not always feel it engage (under load ) then when you step on gas rpms run up until gear catches. No other gear does this and again it threw a vehicle speed sensor code it'* been fixed and still does it so it makes me think it'* electrical or fluid needs to be done and it'* intermittent i just think if it was a trans internal issue this would happen all of the time am I wrong

Who knows, there are a lot of moving parts in a transmission and just because it doesn't malfunction every single time does not necessarily mean the tranny is fine. A fluid + filter change is the first step and should help to answer that question.

If you change fluid/filter, take note of the bottom of pan, looking for metal, be it chunks or sparkles in fluid, clutch material, etc.

Is this more of a "flare" or delayed engagement? Happening only when cold?

I would throw some Seafoam trans tune into the tranmission tonight, drive it until the weekend, and change the oil/filter (throw in some Lucas) this weekend. I still think you have internal mechanical issues (yes, they can be intermittent) but let'* hit it with everything we got and see what happens.

my Buick was the same, tranny shop said tranny was starting to go, suggested to adjust internal bands(I believe) and it may last longer, if the fluid is burnt, changing it is only a temporary solution, you should check and see if having tranny rebuilt now would be cheaper than throwing money at it on different remedies that may not work. its cheaper to have it done early because there would be less damage internally than if you wait until it goes completely, I waited too long on mine. it depends on the value of the car and how long you plan to keep it versus cost of repair