I have a 2004.5 with the automatic,,, I would like to move my shift points to shift sooner than what they are. Right now if I am accellerating i have two hard shifts, first one hits at 40 mph then another at 50 mph,,,, I would like for these 2 shifts to occur at 35 and 42 or 43,,, If I am going down a hill these shift points do occur sooner. I do not use the truck pulling trailers so it would not be a load stress on the tranny,,,, In the gm cars and trucks I could buy a hand held computer and program my own shift points and I was wondering If the same could be done with these tranny's.
If you could get it to shift earlier i believe the fuel mileage would go up for me since I am not pulling a load.
At 40mph is this my converter locking up and the 50mph the overdrive or do I have it backwards,, with me just babying it they both drop the rpm's about 200.

 

I don't think those programmers exist for our trucks yet. You can try adjusting the throttle valve cable. I had to adjust mine to prolong my shifts as they were happening to soon.
On the driver's side of the engine there is a black rectangular plastic cover with a rounded hump on it. It is held in place with two plastic screws. Once the screws are out you pry out the plastic inserts and work the cover off. On the rear side of the rear bracket is a white plastic adjusting tab on the BOTTOM cable. You pry the tab out slightly, notating how far the front side is sticking through the bracket. Once the tab is pryed out simply slide the cable into the box a tiny bit and push the tab back into place. The adjustment is very sensitive so you don't want to slide it too much at once. Test and Tune and replace cover.
Good Luck.....

 

get the mileage flash, it made 1-2-3 closer and 3-4 taller, mileage went up too.