Damn Boost is acting up, any ideas?

[Airpoppoff]

1)
well lets see, i have the t28 turbo and well you can look at the rest of my mods, and the turbo xs boost controller, anyways the car runs 15 psi easily, but when i turn it up more than 15 at any time it never can hold it id like to keep it at 18 but it spikes for a second then down to 12 then back up to 15 maybe 16 im like what the hells going on anyone got any ideas???.

2)
if you guys know the problem is the turbo i am thinkin of getting a new one, ive got an idea but i mean i dont wanna spend over a grand seriously, and i hate lag i dont want lag so let me know what you guys think i want the best turbo for the grand....... thanks alot guys

 

[Silent2g]

boost leaks
check for em

 

[Airpoppoff]

where would i be able to find a boost leak, bov fine, lines all tight and anything else???

 

[Silent2g]

vacuum lines
bov
intercooler pipes
manifold
anything that has air running to it or through it