i don't have any question that tuners make definite power improvements on deisels (speaking from experience).
my greatest interest in the tuner for the small block is the mpg gain that evey tuner manufacturer claims.
at today's fuel prices a 1 mpg improvement on daily driving could pay itself off in as little as 15,000 miles. although that is a long time, i keep my vehicles well over 100k miles. everything staying the same (more likely to go up in $) that is a fuel savings of $1,700 over the life of the vehicle.
very intriguing...