Doesn't seem to me that 2-3 MPG would cover the cost of propane neverless the kit cost. But it sure does sound like fun.
I agree. If you're thinking of adding propane merely to save fuel, you'd have to drive for
a long time to recoup the savings, since the propane fuel itself is an additional expense. I did it for the power increase, and the improvement in the overall driveability of the truck.
If that's your rationale, you won't be dissappointed.