I have an '03 GMC DMAX. It has almost 55K on it. I bought it with 50K on it. It has not been used for heavy towing. I have a 5th wheel, but only towed a few times...so no heavy usage by me or former owner. I just called the local dealer to have maintenance as recommended in owner's manual. It says at 50K (or is it 52K) to have the transmission oil changed. The guy I talked with at the dealer said, "...those Allison transmissions are hard to do...". He did not know how long it would take or how much it would cost. So, does this sound right? Is this an expensive propostion--changing transmission fluid? And is it necessary? I am getting a oil and filter change also. They will be putting in the new fuel filter--this is why I am going to the dealer--I usually go to a local station which does a fine job on my cars. I should say I bought this truck last May and it is my first diesel. This diesel thing is still new to me. I really really like the truck.