Look into the predator progammer. It will do a power boost program and you can fix the speedo problem.
I have my "New to me" 2001 dmax, I just drove 1700+ miles from denver to NJ. I kept the truck stock for the first tank of fuel. MPG was 15.4 and average speed was 75mph on flat land.
I bought the programer and brought it with me and after the first fill up I used it to reprogram for the 40hp gain.
OMG... I could not believe the difference!
More power, faster acceleration, more feel in the seat with lighter foot pressure. And my MPG went up to 17.6 still driving 75-80mph flat thru kansas.
My truck has 155000 miles on it and the injectors were replaced at 145000.
I found this programer on e-bay for around 300 bucks.
Oh, and this will monitor the engine, look at and reset engine codes.
Jeff...
1992 GMC Sierra("2003 TDP Photo Contest Winner") 6.5L Turbo Diesel, 4L80E Auto, 4x4, 3" Body Lift, 33"x12.5"x16.5" Tires, Back Country Nerf Bars, Banks Stinger Kit, Banks Pillar Pod, Banks Boost, Pyro, Trans Gauges, Kennedy Quick Heats, Lube Specialist Oil Lines cooler kit,
2001 GMC Sierra EC K2500 6.6L 4x4 Duramax-Allison Long Bed, Predator 40hp program.