Need help i think i need a new break booster
 

Hey guys. I need some help. I have a 1996 gmc sierra sle 350 v-8 automatic 2wd 1500. I was driving today and pressed the breaks and it was real hard the idle dropped and then got real softed and then was normal but i can hear it hissing the whole time i have my foot on the break and the idle surges. I believe i need a new brake boost right? How hard is it to change. I have changed about 4 of them on my camaro so im familiar with the system but is it almost the same on the truck. Im planing to do this tommorow so if you can please reply soon.
Thanks,
96gmcsierra