I have a 04 gmc sierra 1500 4.8l with automatic trani. I would like to put the standard five speed trani in it. Besides swapping the trani and installing the pedal and linkage, ecu change?

yep whole 9 yards

And wiring harnesses with clutch and tranny sensors. I havent done a swap on a new truck but on the older ones the steering column support had to be changed to mount the pedal, check it out. No linkage, should be hyraulic. I hope your cab has the hole pre-cut, if not maybe make a template from the hole in a manual cab. If you get a donor truck then you should have all of the right parts. If your good with wiring you can get the diagrams and the ECU pinout and modify your existing harness and then get your computer flashed with the manual info. It's easy going to manual, adding all the wires for the 4L60-e would be a nightmare.