I bought a 2006 Monte Carlo LT. It had its issues (leaks in everywhere possible to leak) but I met a pretty knowledgeable guy who spruced it up so all the leaks were patched, cooler lines to trans replaced as trans fluid leaked from there, and clean fluids re-introduced, and it came from a vehicle having some issues into a no-leak having, fastlane driving, properly shifting, no check engine light having son of a gun! For about two weeks! It was fun!

Then one day I'm coming back from a day of fun (getting to work without needing to bum a ride or use public transportation), I stop literally one stoplight before home, and when light turns green I accelerate as normal but the car got up to about 20MPH (3K RPM) and basically instead of shifting into 2nd the car just kept climbing RPMs, almost as if it had a speed limiter or went into neutral, and it will be in that neutral state until speed is under 20, then it's like the teeth start gripping in the drivetrain again until it reaches the shift point... So basically, it's not shifting into 2nd, 3rd, or 4th, no matter how many RPMs I give that first gear. No clinking, clunking, banging, smoking, burning, jerking, no nothing... Just smooth cruising in first gear (until 20 then just stressing the engine trying any more)

Anyone ever experienced this & what was the solution? I would love to enjoy this car. Thanks in advance.

 

First thing I would do, check and make certain it has the appropriate amount of fluid.

If it does, then I hate to say this, these cars have a 4t65e transmission and it is known for issues that include failing to go into gear. If you check the website for a company called Triple Edge Performance, they specialize in these transmissions and might have some go info in their FAQs.

 

Sounds like its time for a rebuild assuming fluid + filter are good.