04 gmc sierra. Warning light for thr booster came on. Shop quoted me 200 for part and 200
for labor. I can get a new replacement for a little over 100. Looks like just 2 bolts under the hood
and 4 in the truck but a tight squeeze. Is this a pretty easy job? Anything I could really F up?

ETA:  I'm a moron and it's early and I read waaaay to fast sorry.. You're asking about the booster, not the master cylinder.  That I've never had to replace......soooo....I'm of no help to you!  



Google "bench bleeding".  I've replaced master cylinders.......but I never did the bench bleeding....it made it really difficult to get all the air out of the system.  Bleeding brakes is my least favorite shade-tree mechanic process.  I hate it and it's difficult to do correctly.  Speed bleeders at the calipers make it easier, but bleeding the master cylinder when replacing it seems to be fairly important.  That's as much as this amateur knows..........

ETA:  Replacing the actual part is very easy.......

Haven't done that model, or anything that new for that matter, but I doubt they've changed much, the ones I've done were pretty easy, seems maybe getting the pedal side linkage undone sucked, but then anything laying on a floorboard between seat and firewall under the column sucks. Dealer book time probably includes pulling the seat, which makes that work allot more pleasant. I say go for it.

Its usually very easy, you just remove the master cylinder from the booster, unbolt it from the firewall, remove the clip to the brake pedal and return sprain the reverse for reinstall. On rare occasion you have to reuse the vacuum fitting, but it's probably model specific.

Do it your self its a easy job.

Easy job.  And you should probably put new brake fluid in the whole system anyway.