Karl,
I have had the Ricksons on my 2000 truck for a couple of years now. In my case there was no noticeable change in mileage. In order to compare pre-installation mileage and post-installation mileage you will have to recalibrate your odometer, or at least make the mathematical correction.
If you keep the truck long enough to wear the tires out, and it looks like you will, you will break even by the time your 19. 5" tires are shot. The savings is from the 3 or 4 sets of 16" tires that you didn't have to buy. After the first set of 19. 5" tires, there is a slight savings over 16".
I didn't notice any significant change in ride characteristics either. My truck rode harshly before, and it still does. But it's a truck.
My truck has the factory installed trailer hitch. I bought four Toyo M-608Z 245/70R19. 5 tires for my wheels, and someone gave me two Michelin XZA 8R19. 5 tires. I'm using one of the Michelins for a spare. It will not fit entirely into the well for the spare tire, but it will ride a bit lopsided in the same location. It has been this way for about two years without any problem. Rickson says that other hitches, that mount to the frame differently allow more clearance, and the 19. 5" tires will fit with those hitches.
My Toyos, at 245/70R19. 5 are about the biggest tire you can install on a stock set-up without rubbing on something.
I think that the only downside is the cost.
I really like mine, and the service from Rickson is outstanding.
Loren