2001 Beetle limp mode

HI guys, I recently purchased a 2001 tdi beetle that needs to pass smog. I started searching here and on the net on the fixes for limp mode issues. the code that I got from the PO was a p1556 low boost signal. I went through the whole program for fixing that code from tdiclub and myturbodiesel. I swapped a 1.6TD in my suzuki samurai, a golf 1.6D na and am comfortable with the mechanical inj motors, TDI/VNT is new to me.

The symptoms are: check engine light comes on about 15 seconds after startup(dirving or idling), low power once it gets to 45 mph( limp mode right?) the code i have is from a obdii not VAG. I looked up the closest VAG mechanic from the map here and the guy doesnt have vag reader anymore. So i wanted to try to fix it my self.

So far I have cleaned the vnt actuator (checked with vac on actuator tube for 1/2" movement), vanes(oven cleaner method), egr, intake manifold, replaced the MAP and MAF sensors, and changed the vac lines. im not sure hos to check if the n75 is working correctly or not. I hear that you can swap it with the valve next to it. Ill try that today but wanted to see if anyone has any other insight for me at this point.

I have an appointment for a VAG diag next week but I thought Id try to get it gong by then if I can. $120.00 for the diag.

I'd guess you have the right code, it's so common.
I would first check if the actuator moves when you start the engine. If it does, I would then check that the actuator just starts open at 3.5 to 5 "/hg (using a vacuum gauge and pump).
Here is a link to the Ross Tech wiki
You've already checked some of this. Swapping the N75 and the N18(?) is useful.

You can rent a vag reader from AARodriquez aka Fixmyvw.com for $5/day, 3 day min and he only counts the time you have it (tracking number shows when you received it).

Just an FYI.
http://www.fixmyvw.com/vcds-hex-can-rental/

thats aweesome guys i think I will rent the vag.
I swapped the n75 for the other one and it made no difference. I also found that that the car ran better in limp mode with the maf sensor disconnected, but it still dropped off after 45 mph

A bad MAF sends incorrect signals to the ECU, which then results in improper fueling. This can/will result in erratic behavior. Unplugging the MAF, dropping the MAF signal to the ECU, causes the ECU to operate based on a static set of data (rather than the signals from the MAF), which should result in a smoother running/operating engine, though with a significant reduction in power (it'll feel like a non-turbo).

You can also look to see if there's a forum member in your area that has VCDS: http://forums.tdiclub.com/showthread.php?t=296841

Make sure you have replaced ALL the vacuum lines elbows etc, wash out the valves (hot water works well though old timey). Be thorough!! Dont skimp! I have found limp mode problems to be mostly linked to vacuum system issues which can be hard to eradicate but cheap.
Perhaps also a new Bosch MAF is needed.