I have bad luck with 4L60Es lately...
 

Converter stopped locking up in my truck Friday. Borrowed my father's Sierra, filled it up this evening. Started to leave the gas station... Bang! The sunshell broke just like my truck. His transmission has barely 20K miles on the rebuild. No 2nd,OD, or reverse. I needed his truck to get to work while I got mine fixed this week. Now his is broken worse than mine. ::sigh::

Monster transmission sells upgraded trans really reasonable. 500 HP jobs and they just about the same price as stock. 1700 or something like that.

I am pulling my truck apart anyway, so I have started to pull his transmission out. I am going pull mine out Friday after work. I already grabbed another converter. I'll make one running truck out of two. lol

The builder made good on the transmission out of my father's Sierra. He rebuilt it and supplied the parts for free. Said it looked brand new inside, other than the busted sun shell.

I guess now he has a good spare transmission. I will never go back to a 4L60E, 4L80Es are just so much more durable.

And the saga continues...

His truck was running great. Then started to miss shift and slip. Took it back, full of metal. Supposedly fixed... converter wouldn't stay locked. I dropped it off almost 2.5 weeks ago, still don't have it back.

We're going to start buying parts for the 4L80E swap in his truck. Tired of these weak transmissions.

Got the GMC back yesterday. Ended up using a completely different case and valve body. So far, so good. I am still leaning towards a 4L80E swap in the future.

Probably not a bad idea. The 4L80E is a much tougher trans. That was the trans in our old motorhome. Moved that motorhome while towing a car, never had a hickup with it. We had a small Blazer before the Trail Blazer with a 4L60E. Blew the sun shield to pieces.

That was short-lived... forward sprag took a dump yesterday. Good thing he has a spare. In the process of swapping it out now. I stressed to him repeatedly - get a 4L80!

Now he is wishing he had. Definitely putting one in their Pro Tour 72' Malibu. No room for mistakes with that car.

Problem solved! Picked up two 4L80Es today.