Badly adjusted TV cables usually murder the 700R4 and I have yet to see one last behind the LS motor without the use of the Bowtie Overdrives adapter (and even that often does not guarantee a proper adjustment). People thing they can eyeball the bracket, but the geometry of the bracket on the TBI and Carb setups has some variance in it at different throttle points that I do not think is properly emulated by all the home brew experts. That being said, if you have access to a 4l80e I would go that route because its just a much stronger transmission and a stock rebuilt 4l80e should outlast a 4l60e by a long shot. You will have to move the cross-member back, shorten the rear driveshaft, and lengthen the front driveshaft. Likewise you will need to make sure you get a 4l80e adapter and either a NP208 that was behind a th400 or take your current one apart and swap in a 32 spline input shaft on your transfer case. After that you do a pin swap in the wiring harness for the 4l80e connector and have your tuner update your tune for the 4l80e (do the segment swap and adjust the shift points). I would recommend going on ahead and having a rear aluminum driveshaft made as well. There is a reason most all the new LS trucks have them, especially the 4x4 trucks with taller gears. The forces involved kind of dictate it.
Likewise you can take a chance with the 4l60e. There were incremental improvements on it beyond what is offered in the 700r4 and those changes make it a better trans overall. the computer also does a much better job of managing pressures and shift points than the manual TV cable ever did on the 700R4.
One thing that will also help, if you have not made this change yet, is bypassing the trans cooler in the radiator and just mounting an independent cooler. A lot of folks never think about it, but running it through the radiator essentially guarantees that your trans fluid will never be less than 170 to 190 degrees as it enters, because that is static temp of the water as it circulates. Moving it out of the radiator will allow it to cool as low as possible and heat is the enemy of any automatic transmission.
