Barry Smith notes that LRR is almost dubious as a reality (if I have not misunderstood him) as across a range of tire choices the mpg effect may or may not coincide with LRR labelling.
I'd spend a good deal of time at TireRack in reading the comments on tires with:
- 20-million miles of survey reports
- For those who have kept the tires in excess of 40k miles
- A tire that places in the top ten categorically
Second, how long one willl keep the vehicle and how many miles it will travel in that time is the most important consideration. MICHELIN is hands down the easy choice for longest lasting truck tires, and this is the better basis for economy over putative "Green" labelling.
While some other brands may be close, I would be looking at others in my climate, terrain and use (also as above) who most closely simulate my projected use to determine the best choice for a work vehicle.
I would spend more time in rebuilding the front end, eliminating steering slop, and replacing bushings (anti roll bars, FF & RR) and installing (at least) BILSTEIN shocks. Bang for the buck comes down to driver feedback and best transient response. Trucks need all they can get. Ergo, even a "lesser" tire will do well with a tight vehicle, and none can overcome one that is worn (100k or just under 10-years that rubber has deteriorated).
2004.0 DODGE Ram QC/LB 2500 2WD/NV-5600 305/555 ISB. 7,940-lb. Stock. 192,000 miles/4,900-hrs @ 39-mph average. 35' 9k GVWR TT. 14.6-cpm solo & 25-cpm towing; 21-mpg average past 44k-miles