can i swap out my 4 speed automatic transmission for a 6 or 8 speed transmission with a lot of trouble? 2004 4x4 Z71 Suburban.

 

Yes, but OMG the issues and electronic problems would deem the benefit as void. The new Trannies are completely electronically controlled.
If you are trying to get better performance or con out of your ride the figure in a tranny kit and consider your rear gears.

 

The transmission seems to be going out. We pull a 31' Airstream trailer so just checking on the options we might have in the event the transmission fails.

 

I would probably stick with the same tranny the 4l80 or if you can get the 4l85 the 85 has more clutch packs and higher pressure and its valve body is designed for firmer shifts.