Recently, my boost gauge has read little to no boost. It will SLOWLY creep to 5 PSI when I floor it in 4th/5th gears, but there is nothing in the lower gears. I checked under the hood and didn't see anything less/disconnected and nothing sounds different. Any ideas where to look?

 

Check and make sure the vac line completely connected to the gauge.
If that's not it maybe someone was messing with your boost controller.

 

Alright, so when I looked under my hood, the air filter had come off where it was attached near the MAF. Would this have caused something in the ECU to go screwy and change the boost?

 

only if it read really funny, but it shouldnt. Have the car scanned for codes

 

And fyi - there is no MBC installed right now, just the normal N75...

 

Oh okay, I was just going by your sig.
Does the car drive like it's only getting 4-5 PSI of boost?
If there's no change in performance, my guess is still on the vac line.

 

It doesn't feel like the turbo is really kicking in at all......doesn't quite have that throw you back in your seat when you floor it feel (if that makes sense).....

 

Even after reconnecting the air filter?
Might want to think about making one of these boost leak detection tool
Some more info

 

Problem still ongoing, but I finally got codes ran, and here's what I've got.....

P0118
P0140
P1113
P1114
P1128

Anything look like a related issue?

 

You at the min have a bad primary o2 sensor