Just went through this in my Buick lacrosse with 4t65e trans. Pretty common issue I think, I replaced the sensors and wiring harness, not too hard or expensive, mine was doing same thing and I took a shot after watching some YouTube videos on the subject, bought all the parts on Amazon for under $200.
Had a floor jack and stands, unhook top motor mounts, take off driver side cradle bolts and loosen rt. ones , you have to jack up driver side so you can remove trans cover, sounds worse than it is, good luck.

 

great! what sensors and what harness. post the link if you have it.

 

Sorry, having trouble with that link, just search for "ac Delco 4t65e 5pc. Solenoid set", it's sold by "trans parts now", comes with genuine ac Delco parts if that's important to you, it was me, then I purchased the "buy all three" which includes the harness, gasket, and filter for$170.85
https://youtu.be/miVKmN3gD6o
Here's a pretty good video of what's involved.

 

so in the video the dude changes the the valve body wiring harness, the shift solenoids and manifold pressure switch.

 

That's right, that's what fixed my issue, one of those or all?
Assuming we're on the same page here, after warming up and driving around for awhile, sitting at a stop, then go to take off the car would rev slightly then slam into gear. Does this sound right?
Also, this wouldn't always happen on que, it was more random day to day.

 

yep, if one of those parts are bad it will cause your issue. I have no issue with replacing it all while you are in there....you don't want to go back in after that much work.

 

my car does this! I was told it needed the trans replaced. Did that and it still does the same thing. Would these be things that should of been replaced when they rebuilt the transmission.

 

That was a really bad rebuild. it is a known GM problem. A valve body could have fixed it, and will if you get the guy to do it. Surely he gave you a warranty. I get my Trannys from StreetSmart. 3 year, unlimited mileage warranty for $2100. This is for the old style 4 speeds.