anytime
the trans tune helps a lot by keeping rpms lower. I am trying to get the most mileage out of it, but still want to be able to drive through terrible mountain roads, and deep snow. I'll be running studded snow tires in the winter, with chains once I'm off-road. I haven't tracked my mileage since the computer was programmed for 32's from the PO (which were too big), but I'm sure I've made some descent gains. More important to me, getting rid of the mech fan made it where I can actually keep an eye on things, work on stuff easily, and removed two or three points of failure + 2 or 3 parts I don't have to pay to replace periodically. If you check the bearings on the fan pulley, unless it has been replaced, I'm willing to bet they are bad on most everyones CRD's. I got one crd that it blew up and the fan ate the radiator. Luckily it didn't destroy anything else. And then, you've got the problem of it overcooling most of the time, because it always runs, especially a problem in the winter.
I also have a warm air intake (just pull the plastic bit off the air-box) which gives a slight mpg gain, and I don't want it sucking cool air, unless I'm towing something really heavy in the summer. So removing the mech fan helped a tiny bit there also.
I'll eventually post my mpg when I've got my new grill block installed, the Turbodieselfreak stat installed, LRR tires, and a gps to track my real mileage.
My goal is to average 30 mpg, and that's with a lot of offroading. Probably won't get there, but maybe I can get a 40+ mpg tank at 60mph on the highway someday.