I have a 2001 2500 with 125000 mi.The Automatic transmission has to warm up for several minutes before it will engage. The level is always fine and it shifts well once its warm. I put a code reader on it and received a p1740 code which is a manual control issue but I can not find any more than that.Also I would like to know what the average fuel mileage is for other owners
I believe this is caused by an internal transmission seal leaking. I had a car (was a 1980 Chrysler with a 727 trans) that behaved very much like your truck does. Except mine wouldn’t go into reverse when it was cold, and would lag shifting into 2nd until it warmed up a little. When I bought the car, it had sat for over a year without running, and I believe the tranny seals had dried up and shrunk. After about a year of driving it, the problem lessened until it essentially went away. I think (not positive) that the heavy-duty transmission in your truck may be loosely based on the older, nearly indestructible 727. It may be possible to replace the seal without pulling the transmission, but I wouldn’t count on it. Perhaps Transman or someone else with some knowledge of these transmissions could confirm my diagnosis/give you info on what needs to be done.
As far as mileage, I had a 1500 with a 5.9L which consistently gave 11 mpg in the city, winter or summer, a/c on or off. On the highway it would get up to 16. I had a 4WD with bigger tires than stock and a little lighter truck than yours and it was tuned well. I wouldn’t expect any better mileage than this really. Maybe you could squeak it up to 13 or so if you baby it all the time.
There was a TSB on this condition. It requires replacement of the pressure boost valve plate inside the transmission. That could very well be the reason you are getting this code.