My lil old 4l60e is on its last leg of life. Just in the last week i have had 3 different SES lights all sayin "malfuction transmission control", random downshifts, frequent hard shifts, and even on the way home from a fishing trip pulling the boat it chirped the tires through all 4 gears. So seeing as how i had a shift kit and servo order and had to cancel. Not gonna dump a bunch of money into a dying tranny. Anyway i want a fully built HD 4L80E. Reason for this is i want to get a Nelson Tune and have most if not all of the torque management removed, and im told that would destroy a stock 4l60e within a day. So anyway my questions are where is a good place to get a built remanufactured trans? and also will a 4L80E bolt right in place of mine or will there have to be any sort of modifications?

Can't help you with where to get one, but i believe it should bolt up directly. I was told that any V-style engine 4.3L and up will take the same tranny.

Check on eBay for trans. I would say the wiring and computer may be a bit different though but not positive.

Yep, I have also heard that all V engines in these trucks will hook up with either tranny. I know that the 4L80E definitely matches engines from the 383 to 454 range very well. So I'm sure a 350 will be ok.

I think you have to move your transmision support braket back some cuz 4l80e are longer.