4l60e question

[MMLX89]

I just picked up an LS swapped 72 C10 a couple of weeks ago. Current running gear is 5.3l backed by 4l60e trans. On my way to work Friday the trans let go. Started with a whining sound, ended with horrible grinding, clunking, and felt like someone slammed on the brakes. No forward gears currently, but reverse still works.

As I started looking into a replacement, one shop is telling me that until I swap over the rear-end from the same vehicle (2003 SIlverado), that I will continue to go through transmissions. The speed sensor and associated parts won't read things correctly, etc.

This seems a bit far fetched to me, but wanted to get your opinions...