Final word on the gear change. I towed the 24 foot 4700 lb plus trailer 2 and a half hours today and got 13 mpg a big change from the 8.2 that I got before the gear swap. The truck also stayed in 6th gear instead of not getting out of 4th. It cost alot to get it done but in my opinion well worth the money.
OH YA driving empty at the same speed raised the rpm's by 400 rpm and managed an extra 5 mpg.
I think the 4:56 might be better for the towing part but non towing I think the rpm's would be to high