I have a 2009 4500 with an AS68RC that will go into limp-in mode if I don't ease away from a stop light or sign. A mechanic scanned it and told me it needed a couple of solenoids I replaced all four but it didn't help. What did help, for a few days anyway, was changing the fuel filter. Which was really bad. I thought it was fixed but no. So now I'm wondering if I have a low fuel pressure issue and need to replace the pump. Or maybe a short in the trans harness. Or maybe a computer problem. Or maybe I need to replace the pressure switches in the trans.
Any help or suggestions would be appreciated.

 

I'm not sure anyone reads this forum anymore, but I wanted to let those that have the same problem know in my case it turned out to be a bad "fuel pressure relief valve". Located on the fuel rail. There are several videos of it on YouTube.

 

how did you fix this issue ?

 

I replaced the fuel pressure relief valve, no help. I replaced the fuel pressure regulator (on the back of the fuel pump), no help. Then I replaced the fuel pressure sensor (on the back end of the fuel rail), that did it.