Gas trucks are way overgeared these days, and that is strictly so suburban cowboy commando commuters (like me) make enough empty mpgs to keep the EPA happy. It is liberating to dispense with the notion that the gasser is supposed to cruise towing at the same rpms as unloaded, and understand that 4000 rpm or more isn't the end of the world when climbing. Let 'er eat. Compare torque peak rpms of your newer gasser with your Duramax, and then see how that plays into the empty cruise and towing RPM conversation. There is no way I'd own a gas pickup with diff gearing higher than 4:10s. Ford supplied some V10 superduty trucks with 4:30s instead of 3.73s, and they have reputations as strong trucks when so geared.
I have a 7.3 diesel and a stick (because I'm a control freak) in my '99 ford, but if forced to buy new gas, would look for whomever has the best combo of gearing and doesn't derate or pull power for shifting (as GM has done with gassers/autos in the past).
I realize that newer auto's are better about this...but it bugs the crap out of me to listen to an automatic transmission try to find a gear in which it can lock the converter and not roast itself, diesel or gas. Moreso when towing heavy stuff on logging roads (btdt, with 454/4L80E 3/4 ton suburban). Any auto is going to hunt for it's EPA-driven optimal gear at all times, tow/haul or not, rather than just sticking it out at 4500 rpm for the duration of the climb, or 3000 rpm for the duration of the twists/turns/ups/downs. What a PITA.
The high water mark for gas pickups are the 6.0/NV4500 GMs and the V10/ZF6 fords, but the standard transmissions got shelved a decade ago. Maybe dodge has/had a similar OD stick for the hemi, IDK. Depressing. Makes a guy want to build a tow/haul only pre-EFI GM crewcab truck with a carb'd 454 of proper compression (9.0:1 to 9.5:1) and appropriate cam timing (210 to 220 at 0.050"), 4.56 gears and an NV4500 or spicer med duty standard trans. It would be fun to compare loaded economy with such a critter against a newer truck. Buy a milsurp K30 for the 4.56 axles (14-bolt FF and dana 60), a good 2WD pre-87 GM crewcab, and marry the two...
