I have a 2003 2500 with the 48re trans. Recently bought it with 133,xxx on it and have put 6,000 on it since. As far as performance the exhaust is strait through, k&n filter and a Dr. Performance module. I do know the guy pulled his gooseneck with it and thats it.

So today I was hauling feed in an enclosed trailer around 7,000 pounds total. As soon as i got on the road my rpms went to 3000 and the trans was slipping bad it wouldn't shift until i let off and it would only let me get up to 50mph doing 3500 rpms. no power and the tc wouldn't lock in. Went to the gas station and dropped the trailer and got my dad to pick it up. I drove it home and it would shift perfect. Got on the freeway and it would hold all the power. Once my tc was locked in I got on it and no slippage. So I was wondering whats wrong with it? Is it just going to et go one day? I have no mechanical experience and am somewhat mechanically inclined. Just want to know if I need to get it rebuilt and what it could possibly be. Thank you, also I'm new to the forums

 

man i have the same thing goin on in my '06 but with just over 131k on it, and 35" tires and that's it. started acting up doing the same thing the other day but not hauling a trailer. transfer case doesn't want to lock up either. some kind of linkage or belt in it is slipping when i put any throttle on it.
if it aint one thing with the truck it's another.....i'm having a guy i trust with an '06 dually used for towing check mine out. and if no one else responds i'll letcha know what he says...

 

Yea, mine shifts fine as long as its not under a load. I don't know if it will last though

 

Get yerself a new converter and valvebody. Clutches probably are facked as well.