Honestly, with your current trap speed 105 mph, you aren't doing too bad with 12.8 ET's. You could probably shave a tenth or two, but why put your truck through all that heavy hard launch drama when you could just add more power for the same price as a new set of fancy wheels or tires?
Do you have cal-tracs or traction bars on the rear? Have you tried playing with your current tire pressures? I've seen well setup trucks cut 1.7x 60' times all day long on stock Dodge Michelin LTX tires. I've seen 100% stock suspension Dodges cut 1.80 to 1.85 60' times all day long with stock Michelin tires at 30-35 psi.
Surely your lighter weight Dmax can manage the same type of 60' times. Call up Rob Coddens at ATP, he lives and breathes Chevy Truck drag racing suspension, tuning, and tires, he'd be a worthwhile phone call. I'll bet he has several stock suspension D-max trucks running consistent 1.6x 60' times.