Transmission slipping into neutral at lights

I am thinking its time for a rebuild but i wanted to get some expert opinions from those that have delt with transmissions, i have 0 experience with the insides of them.
After installing my I/C and dropping down to a 3.2 pulley my tq has pretty much exceed what a 180k mile stock 4T60E can handle. My 1-2 shift is set at 53mph and 5500rpm. It is over revving to 6300 and 60+mph and still doesnt shift sometimes. I have to let off the gas briefly to let it shift and then its fine. When it does shift at WOT its like its neutral revving and slamming into the next gear. NOT GOOD.

So, i pulled the pan and changed the fluid (had 30k on it). Pic of fluid and magnet as it came out. Really not that bad IMO.


Put in a WIX filter and filled it up with dexron 6. I did not flush it.

It shifts much better at WOT now BUT, now i am having an issue where when its really hot out and trans temps get up there it will slip into neutral coming to a light. I can rev it up and get nothing to the wheels. I hear a whistle/whine from the trans when it slips up. Dropping it into 1st doesnt help but if i put the shifter into N and then back to D it will shift back into drive and be ok for a few more lights.

What part is breaking that would cause this? Maybe i just need another shift modulator??
If i get it rebuilt are there any HD internal parts for the 4T60E? Will aftermarket 245mm converters work?

I say just rebuild the damn thing and get it over with. There are TONS of parts available for that trans....including a bigger gear with POSI
If you're serious bout buildin it, I can point you to the right stuff online.

im serious about building it but i am a college kid so i must budget myself.
I would be ok is it was around $2000 for everything installed and i do have a local shop that is very good at rebuilds.
I really dont want to tackle this myself since i dont have a trans jack or a motor hoist.

Well hell.....find a trans at the junkyard and have it rebuilt. This way, your car won't be down for so long. When the "new" one is done, swap it out. That's how I'd do it anyway.....

So what parts would you recommend throwing into it and are the TC's the same as the 4T65's?

Dammit, I forgot you have the 4T60E......I'm looking at parts right now for it. The 4T60 shares parts with the 440T4 and the 4T65. Yes, there are HD parts available for the 4T60E. I'll do some research for ya before I get back to you on it.

That is the delima i have been facing in trying to find performance parts. I know there is a good shift kit for it, but that is about it that i have been seeing. Thanks for the help thus far.

Anyone know what is going bad in my trans? If i know what it is maybe i can prolong the life of it until the rebuild is done and i can be sure to get a upgraded parts.

You have a scanner? If you do, monitor the gear selection and the line pressures to see what it's doing. Sounds like the 1-2 solenoid may be shit. Once it's in gear and driving, do all the other gears work ok?

Never had a problem shifting 2-3 at WOT, and that shift point has been raised.
If the 1-2 solenoid is sticking would it cause the car to drop into neutral at idle?

edit: also no problems shifting 1-2 at any throttle position under 95%

also, i am assuming it is dropping into neutral since when i start giving it gas nothing happens. it could be trying to start in 2nd or 3rd gear. i dont want to jump on the gas too much when its messing up since it jumps into gear whenever it want to. (dont want to launch into the car in front of me at a light lol)

I'm just goin by what I've seen. I'm no trans tech....trust me. Aside from diagnosing the electrical side of one, and replacing the solenoids and such, I know dick about transmissions lol. I have a buddy of mine (from the Buick dealer) who's a trans guy. I'll call him in the morning and ask him what your symptom points to.

i appreciate the help. If you need anything from a junk yard let me know and ill see what i can grab you when i am looking for a used 4T60E.

Sorry to hear this, Matthew. At 180k with your mods, your trans has lasted longer than most!

It's strange, but there comes a point when you've replaced enough parts, the car seems to feel almost "new again". I think you'll be at that point after the new trans.

Recheck your fluid level with your car warm. If your loss of power to the wheels condition at idle started after the fluid change, it could be low fluid. I would also think a bad vacuum modulator could cause the shifting problem if letting off the gas will allow it to shift. Hopefully this could buy you some time to find a used tranny and rebuild it. Then swap it out when its convenient. Also a tranny cooler may help if you dont already have one.

Aaron, I agree that its getting to the point that everything is new. I like to think the car is now re-engineered to be better than factory since the mods and replacement parts are done to fit my needs.

Dave, I will be installing a trans cooler at the rear of the car with a fan when i get the new trans in. Im going to replace the modulator just for shits and giggles today and see if it makes a difference. last time it went bad i had fluid weeping out the front diaphragm, but its dry this time (doesnt me its not broke though). Will check the level again, but i had it spot on after the change and its not really leaking.

I called him. I described what was going on, and that you had done a filter change and the symptoms changed.....he immediately suggested monitoring all the solenoids with a scan tool lol. I said that probably wasn't possible. In a nutshell, you either have a solenoid going bad, or some debris stuck in the valve body somewhere. Either way, the side cover would have to be removed to clean it. I asked about a flush (a real one with a machine), and he said it certainly won't hurt.....

Thanks for checking that for me Scott.

just took a video and im still having a problem with the 1-2 shift. Fluid level is OK and i just bought a new modulator that will go in later today.
its 85° outside and i was hitting it from a turn so dont hate. just wanted to show what the 1-2 shift was like. Again pcm set to shift at 5500rpm