I found this site on Google, the thread was all about 4l60e transmissions and what would fit with what. I left a reply on that thread. It just seems like it's a dead thread though. I replied to a guy who replied last year, anyway... I have to pick the brain of anyone who knows this, so I'm just going to paste what I replied on the other thread. I hope it's ok.....

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I've looked all over google, found similar problems that I am having, however I yet to have a solution. This topic, this thread seems to be what can help me the most.

I have a 99 Tahoe with a 4l60e transmission that went bad. So my friend says he has a 98 suburban that he is about to part out, he swears the transmission will work in mine. So I decide to try it.

OK so my transmission has the whole bell housing and his only has half of the bell housing. This visually is the only difference. Which might be the big difference, IDK but they both bolt up the same. Did I mention they're both 4wd? The difference in the transfer case, mines in the floor, his is push button. We had to swap the sun shellcto put my transfer case back in.

OK so now I have his transmission bolted to my motor, and transfer case. All the plugs are the same. Ready to crank it up and try it... And here's where the moment of truth is.

It cranks fine, it idles fine. But when you put it in any gear the torque converter locks up. Now I know a jam up mechanic, that says go to your main plug and compare his and mine. He said there's going to be a difference in one wire, he says it's likely one pin off and causing this tcc issue. I have no idea, but from what I goggled it's a tcc solenoid problem. Can anyone please help me figure this out.

 

Unplug the trans first.....If it no longer stalls.....You have the harness pinched somewhere/TCC PWM circuit is grounded.

'98 & '99 4L60E's are electrically compatible with each other....Even though the cases are different.

 

I've tried that, it still locked up. I was wrong on the year of the suburban, it's a 97 not a 98. I was told today by a mechanic that also builds transmissions that I probably have the wrong torque converter. I used the one from the suburban, do you know if there's a difference? I already started the process of taking it out to see for myself. Also when I said sun shell, I actually meant the transfer case adapter plate.

 

For the sake of this thread.....'96-'08 4L60E's are compatible with your PCM.

This is a 5.7L Gen 1 Vortec? There are different 298mm torque converters (Clutch material differences). The TCC will not stay engaged from this difference alone. The apply strategy may cause a paper based friction to fail if your calibration requires a woven carbon based friction.

Did you replace the O-ring on the Turbine/Input Shaft? Or at least inspect it?

This is what happens when you buy a piece of **** trying to save a dollar.