With the T-5 you're likely to have one too many gears unless the land you're traveling is flat as a pool table. Downshifting for even a small hill gets old in a hurry.
When I set up my van for long distance highway travel, I installed one inch bigger wheels (14 to 15) and chose a tire that gave me an overall tire height about 2" taller than the original 14" tire/wheel setup. The ideal cruise speed for the best gas mileage is around 70 MPH now, as long as the terrain is relatively flat- - - - -great for most interstates. I've got a Ford AOD transmission behind a 3.0 L V6 in an Aerostar van. It has four available cruise ratios- - - - -3rd. gear (direct drive) with the torque converter clutch engaged or disengaged, and the same options in 4th. (overdrive) gear. Locking/unlocking the torque converter is a matter of stepping on the gas just a little to raise the TV pressure and disengage the converter clutch, which changes engine RPM by about 10% . On 55 MPH 2 lane roads, the ideal gear is direct drive with the TCC engaged, done by a manual shift out of OD. High gear, with the TCC in or out, is too high.
The trick is to get the engine on the "sweet spot", RPM and torque-wise, regardless of which gear you happen to use. A T-5 and a 3.42 gear might be a bit too high for good performance and gas mileage, depending on your choice of tires.
Jerry
