I have confirmation that the problem with the older LQ4 blocks from '99 and '00 trucks CAN be fixed so that you can use a 4L60E as well as a T56 from an LSX car.

The blocks are identical between the older and newer LQ4 blocks, it's simply the crankshaft that is different. Swapping out the crank for that of a newer LQ4, LQ9, or even an LSX car will cure the problem. I got a private message from a guy on cfmperformance.net that a good friend of his had this problem and fixed it by putting an LQ9 crank in it and now he's using a T56 behind his motor.

Here's a link to the "problem" originally encountered with this motor.

https://www.thirdgen.org/forums/ltx-...0-lq4-6-a.html

So if you've got a '99 or '00 block and you want that 4L60E or a T56, there is a solution!

 

Yeah, we found out the hard way that the LQ4 is .44" longer than the later LQ4, 5.3's and such. Broke the pump in our 4L60E, mushroomed the converter, and took us 5 hours to get it out of the transmission.

 

Yea that's a rough way to find out for sure.