I wouldn't switch the leads at the same time you are reworking the curve unless you know its backwords.
Yes, switch to manifold source if the current setup is causing the coolant temps to rise and not stabilize at idle. Not toalking about the usually rise that accompanies the reduction in airflow when coming to a stop.
I also filled it up with gas and this past tank only got 8.5 MPG, the horrible gas mileage is another reason I've been making myself crazy trying to get the tune just right. I've already gone through the carb and know that's good (tuned Edelbrock AVS2).
I guess "horrible" is a relative term, it is after all a 3/4-ton truck and has 33" tires with fairly aggressive all-terrain tread pattern. Based on what most people over at Ramchargercentral tend to get on their old Dodge trucks though I think it should be more like 12-14 MPG. I know it also doesn't help I have a hard time keeping it below 70 mph on the freeway,
Well there's part of your answer! And unlike your car, 70 mph probbaly hurts milage vs. 60 mph.
Also any time spent idling, tuning, etc is a gas milage killer. The mpg of both my vehicles plummets when driving in the city. Literally more time spent idling than moving.
All these things add up.