[mrein3]

Like others are saying, do the math.

850 miles round trip. Assume 10 mpg with current setup. 85 gallons total.

The last tank I bought here was $3.859/gallon for regular unleaded.
85*3.859 = $328.02 for fuel.

Assume 30% increase with .7 OD in 700R4. 850 / 13 = 65.39 gallons. 65.39*3.859 = $252.32.

If you do it once that is $1500 you spent to save $75.70.

You need to make that trip 20 times to pay for the tranny swap.

If I was doing it once I'd stay off the freeway and keep the current tranny.

All that being said I wouldn't mind having a 700r4 in my rig to cut down on road noise associated with my 3.73s rolling down the slab at 70mph.