I just completed some repairs to my 2006 3500 Dodge diesel. It has 200k miles on it. The tranny was rebuilt by a local shop about 5 years ago by the last owner at around 35k miles ago. He had the billet converter installed as well as adding extra coolers. I used the truck to pick a car I bought in Houston, TX last November. We made the trip with no issues, and I have been driving it nearly every day since. In late August I parked the truck to do some work on it and then got sent out of state on a project. I worked on the truck on the weekends when I was home and finished it up yesterday. The work I did was replace the AC compressor and dryer and flush system, replace w/p, t-stat, idler, tensioner, belt, and fan clutch (with Ford viscous) and both batteries. That's enough history so here is the issue. I started it up yesterday for the first time. When I put the trans in drive it goes to second gear. I can manually shift it to first to get it into low and when I start off and put it back in drive it will only upshift to second. I have no 3rd or 4th gear. The oil is clean and is not burnt. Like a said when I parked it, it worked great. Any thoughts would be appreciated. Thank you!

 

That is really hard to diagnosis. I had my 48RE gone through about 4 years ago, but maybe only 25K miles. I change the fluid and filter every year because like you I tow heavy. It really sounds like you need to get it into a shop and get it checked out. Any good tranny shops in your area? One thing that just came to mind, a good 48RE tranny shop will have a dummy tranny harness to hook up to the canon plug on the upper part of the tranny. It could rule out some wiring or shift solenoids without tearing into the tranny.