The tires on the 19.5s are the same diameter as what was on there before. So no, no change in rpm or mileage. I plan on going with a 245/70 when I buy tires and the are about 1 1/2" larger so rpm should drop about 3-400.
Man that sucks you have to tear it apart again
I have a OBS van turbo in the garage I was going to see if you wanted, but you have the turbo under control already.