'03 with a couple stupid problems

i recently just purchased a 03 single cab 4.8l 5 speed with 65,000 miles

im having 2 problems

First....
it just started giving me a "service brake booster" message

the truck stops fine and doesnt seem to be low on brake fluid, im hoping its just a quick fix, cause i sure hate the dealers

second....
I drove my chevy today and i noticed while doin like 20 in my neighbor hood that my tach was at 6,000rpm!! i was like wtf and quickly shifted to nuetral and then the truck only went down to 4,500rpm. i drove back to my house and shut it off while off the tach was at 3,000rpm!

im kinda stumped, im guessing its probally a sensor issue or what but idk any ideas

http://www.streetsourcemag.com/uploads/Ownerprofiles/puponair/7152006114624PM39391.jpg

They may be related problems. I've seen similar erratic gauge problems with poorly connected I/P connectors (the cluster will have to come out of the dash).

They may be related problems. I've seen similar erratic gauge problems with poorly connected I/P connectors (the cluster will have to come out of the dash).
thx for the info any little bit helps