i have a 4" lift on my 90 suburban right now and in the future i would like to go up to a 6-8" lift. i think ive read on here that the most you can get away with the stock driveshafts is 5". are there companies that sell driveshafts already extended, or do i need to send mine out? what are good companies to use? and the most important question- how much should both drive shaft be extended. thanks for any help.