Hi DA BIG ONE;

Thankes for all the great input about gear changes. Your shift points changed on a per MPH basis but I bet are about the same on a RPM basis, that's what happened with me when I changed to 3.42's. This makes sense for the tranny controller isn't concerned about speed across the ground but engine speed for shifting. OD lock up happens about 1600 RPM if I am using very modest acceloration. That was about 47 -48 MPH with the 3.73 gears now OD lockup happens about 52-53 MPH with 3.42 gears but still 1600 RPM.
If lock up happened for you still ~ 45 mph that would be too low of RPMs and would "lug" the engine. It appears your thining in MPH's instead of RPM's.

I hope this helps you out. I appreciate you tire size observations it has helped me from going to a larger tires.