The map sensor is a good idea. I've tuned with both PSI and load... while PSI is slightly a bit easier to tune, its basically the same idea as load. You still have error correction with PSI. Once everything is set up with the map sensor, evoscan etc... its pretty easy for the most part. Even with 50's in the WGDC you could be in the 20 psi range... so I would start low (like 20's). You'll find that the GM 3 port is very responsive and boost increases fast just with a few changes. I've always used a resistor in my harnesses, but a lot of people have run without them just fine as well. You have the option of getting one with the spoolin up harness.